Bump amqp-client from 5.6.0 to 5.7.0 in /core (#1367)

Bumps [amqp-client](https://github.com/rabbitmq/rabbitmq-java-client) from 5.6.0 to 5.7.0.
<details>
<summary>Release notes</summary>

*Sourced from [amqp-client's releases](https://github.com/rabbitmq/rabbitmq-java-client/releases).*

> ## 5.7.0
> # Changes between 5.6.0 and 5.7.0
> 
> This is a minor release with usability improvements and dependency upgrades. All users of the 5.x.x series are encouraged to upgrade to this version.
> 
> ## Improve logging for TLS connections
> 
> GitHub issue: [#441](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/441)
> 
> ## Don't panic when cancelling an unknown consumer
> 
> GitHub issue: [#525](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/525)
> 
> ## Bump dependencies
> 
> GitHub issue: [#607](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/607) 
> 
> ## 5.7.0.RC1
> # Changes between 5.6.0 and 5.7.0.RC1
> 
> This is a pre-release for 5.7.0, a maintenance release with usability improvements and dependency upgrades. All users of the 5.x.x series are encouraged to test this version.
> 
> ## Improve logging for TLS connections
> 
> GitHub issue: [#441](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/441)
> 
> ## Don't panic when cancelling an unknown consumer
> 
> GitHub issue: [#525](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/525)
> 
> ## Bump dependencies
> 
> GitHub issue: [#607](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/607) 
</details>
<details>
<summary>Changelog</summary>

*Sourced from [amqp-client's changelog](https://github.com/rabbitmq/rabbitmq-java-client/blob/v5.7.0/release-versions.txt).*

> RELEASE_VERSION="5.7.0"
> DEVELOPMENT_VERSION="5.8.0-SNAPSHOT"
</details>
<details>
<summary>Commits</summary>

- [`57aa724`](rabbitmq/rabbitmq-java-client@57aa724) [maven-release-plugin] prepare release v5.7.0
- [`1928ce8`](rabbitmq/rabbitmq-java-client@1928ce8) Set release version to 5.7.0
- [`9f2dffe`](rabbitmq/rabbitmq-java-client@9f2dffe) [maven-release-plugin] prepare for next development iteration
- [`e79ed4d`](rabbitmq/rabbitmq-java-client@e79ed4d) [maven-release-plugin] prepare release v5.7.0.RC1
- [`bb8f6ed`](rabbitmq/rabbitmq-java-client@bb8f6ed) Bump test dependencies
- [`953d255`](rabbitmq/rabbitmq-java-client@953d255) Bump dependencies
- [`e49f66d`](rabbitmq/rabbitmq-java-client@e49f66d) Add comment to explain decision tree
- [`365dd22`](rabbitmq/rabbitmq-java-client@365dd22) Add test for Channel#basicCancel with unknown consumer tag
- [`6081628`](rabbitmq/rabbitmq-java-client@6081628) Log warning when receiving basic.cancel for unknown consumer
- [`be57b26`](rabbitmq/rabbitmq-java-client@be57b26) Merge pull request [#548](https://github-redirect.dependabot.com/rabbitmq/rabbitmq-java-client/issues/548) from spring-operator/polish-urls-apache-license-5.x.x...
- Additional commits viewable in [compare view](rabbitmq/rabbitmq-java-client@v5.6.0...v5.7.0)
</details>
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</details>

core/build.gradle

@@ -102,7 +102,7 @@ dependencies {
 
     testCompile 'org.apache.httpcomponents:httpclient:4.5.8'
     testCompile 'redis.clients:jedis:3.0.1'
-    testCompile 'com.rabbitmq:amqp-client:5.6.0'
+    testCompile 'com.rabbitmq:amqp-client:5.7.0'
     testCompile 'org.mongodb:mongo-java-driver:3.10.1'
     testCompile ('org.mockito:mockito-core:2.26.0') {
         exclude(module: 'hamcrest-core')