deps: update core dependencies (#263)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [io.grpc:grpc-bom](https://github.com/grpc/grpc-java) | minor | `1.30.2` -> `1.31.0` |
| [com.google.api:gax-bom](https://github.com/googleapis/gax-java) | minor | `1.57.1` -> `1.58.2` |

---

### Release Notes

<details>
<summary>grpc/grpc-java</summary>

### [`v1.31.0`](https://github.com/grpc/grpc-java/releases/v1.31.0)

[Compare Source](https://github.com/grpc/grpc-java/compare/v1.30.2...v1.31.0)

#### API Changes

-   api: `ManagedChannelBuilder.nameResolverFactory` is now marked deprecated. It has long been our plan to remove the function, but was not communicated. Most usages should be able to globally register via the SPI mechanism or `NameResolverRegistry.register()`. There is a plan to add a method to `ManagedChannelBuilder` to specify the default target scheme for the channel. If your use-case is not covered, please inform us on [#&#8203;7133](https://github.com/grpc/grpc-java/issues/7133)

#### New Features

-   The following new xDS functionality is added in this release:
    -   Requests matching based on [path](https://www.envoyproxy.io/docs/envoy/latest/api-v2/api/v2/route/route_components.proto#route-routematch) (prefix, full path and safe regex) and [headers](https://www.envoyproxy.io/docs/envoy/latest/api-v2/api/v2/route/route_components.proto#route-headermatcher).
    -   Requests routing to multiple clusters based on [weights](https://www.envoyproxy.io/docs/envoy/latest/api-v2/api/v2/route/route_components.proto#route-weightedcluster).
    -   The xDS features supported in a given release are documented [here](https://github.com/grpc/grpc/blob/master/doc/grpc_xds_features.md).
-   api: Added `LoadBalancer.Helper.createResolvingOobChannelBuilder()`. It is similar to `LoadBalancer.Helper.createResolvingOobChannel()` except allows configuring the channel ([#&#8203;7136](https://github.com/grpc/grpc-java/issues/7136))

#### Bug Fixes

-   netty: return status code unavailable when netty channel has unresolved InetSocketAddress ([#&#8203;7023](https://github.com/grpc/grpc-java/issues/7023))
-   core: fix a bug that a call may hang when using manual flow control and gRPC retry is enabled ([#&#8203;6817](https://github.com/grpc/grpc-java/issues/6817))

#### Documentation

-   stub: Documented more behavior of ClientCalls and ServerCalls, with regard to ClientResponseObserver, ClientCallStreamObserver, ServerCallStreamObserver, and exceptions
-   api: Documented how Providers may be used in their respective class documentation. Previously you “just had to know” the SPI mechanism was available

#### Dependencies

-   Update guava to 29.0 ([#&#8203;7079](https://github.com/grpc/grpc-java/issues/7079))

#### Examples

-   examples: Add client/server retrying example via service config [#&#8203;7111](https://github.com/grpc/grpc-java/issues/7111)

#### Acknowledgements

[@&#8203;alexanderscott](https://github.com/alexanderscott) 
[@&#8203;AnarSultanov](https://github.com/AnarSultanov)
[@&#8203;cindyxue](https://github.com/cindyxue)
[@&#8203;d-reidenbach](https://github.com/d-reidenbach)
[@&#8203;elharo](https://github.com/elharo)
[@&#8203;gsharma](https://github.com/gsharma)
[@&#8203;reggiemcdonald](https://github.com/reggiemcdonald)

</details>

<details>
<summary>googleapis/gax-java</summary>

### [`v1.58.2`](https://github.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1582-httpswwwgithubcomgoogleapisgax-javacomparev1581v1582-2020-08-07)

[Compare Source](https://github.com/googleapis/gax-java/compare/v1.58.1...v1.58.2)

### [`v1.58.1`](https://github.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1581-httpswwwgithubcomgoogleapisgax-javacomparev1580v1581-2020-08-06)

[Compare Source](https://github.com/googleapis/gax-java/compare/v1.58.0...v1.58.1)

### [`v1.58.0`](https://github.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1580-httpswwwgithubcomgoogleapisgax-javacomparev1572v1580-2020-07-31)

[Compare Source](https://github.com/googleapis/gax-java/compare/v1.57.1...v1.58.0)

##### Features

-   add retry logging ([#&#8203;1160](https://www.github.com/googleapis/gax-java/issues/1160)) ([1575715](https://www.github.com/googleapis/gax-java/commit/15757151d4965276bd01e6772c10288959bb17ec))
-   enable setting quota_project_id ([#&#8203;1128](https://www.github.com/googleapis/gax-java/issues/1128)) ([20bb200](https://www.github.com/googleapis/gax-java/commit/20bb200c8019ad1df8acbfe210cea7d5e9a9a57c))
-   non-retryable RPCs use totalTimeout ([#&#8203;1149](https://www.github.com/googleapis/gax-java/issues/1149)) ([b7646a3](https://www.github.com/googleapis/gax-java/commit/b7646a3a959b7e5ef40158851f26ce6701da8ca4))

##### Bug Fixes

-   retain context timeouts in ServerStreamingAttemptCallable ([#&#8203;1155](https://www.github.com/googleapis/gax-java/issues/1155)) ([461ff84](https://www.github.com/googleapis/gax-java/commit/461ff846ca551c2242bf6c60e61234997d0ba58e))

##### [1.57.2](https://www.github.com/googleapis/gax-java/compare/v1.57.1...v1.57.2) (2020-07-21)

##### Bug Fixes

-   Fix javadoc generation on Java11 ([#&#8203;1145](https://www.github.com/googleapis/gax-java/issues/1145)) ([c7a039e](https://www.github.com/googleapis/gax-java/commit/c7a039e07be02298d9dd906b08e1e1bb995e85e2))
-   Preconditions only supports %s format ([#&#8203;1153](https://www.github.com/googleapis/gax-java/issues/1153)) ([8145311](https://www.github.com/googleapis/gax-java/commit/8145311b38fdd3bf82a4958f8aef5313857b70c0))

##### [1.57.1](https://www.github.com/googleapis/gax-java/compare/v1.57.0...v1.57.1) (2020-07-07)

##### Bug Fixes

-   add back javax.annotation dependency ([#&#8203;1129](https://www.github.com/googleapis/gax-java/issues/1129)) ([77a4cc3](https://www.github.com/googleapis/gax-java/commit/77a4cc373914396dd343891e38cf743166668c96))

##### Dependencies

-   update google-auth-library to 0.21.0 ([#&#8203;1134](https://www.github.com/googleapis/gax-java/issues/1134)) ([6528e5c](https://www.github.com/googleapis/gax-java/commit/6528e5cb9cec50ef01c0d2601c6db518df825747))

</details>

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pom.xml

@@ -151,14 +151,14 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <github.global.server>github</github.global.server>
     <site.installationModule>google-cloud-core-parent</site.installationModule>
-    <gax.version>1.57.1</gax.version>
+    <gax.version>1.58.2</gax.version>
     <google.api-common.version>1.10.0</google.api-common.version>
     <google.common-protos.version>1.18.1</google.common-protos.version>
     <google.iam.version>0.13.0</google.iam.version>
     <google.auth.version>0.21.1</google.auth.version>
     <google.api.version>1.30.10</google.api.version>
     <google.http.version>1.36.0</google.http.version>
-    <grpc.version>1.30.2</grpc.version>
+    <grpc.version>1.31.0</grpc.version>
     <protobuf.version>3.12.4</protobuf.version>
     <opencensus.version>0.24.0</opencensus.version>
     <annotations-api.version>1.3.2</annotations-api.version>