Bump pub revision in DEPS

New commits included in this revision:
```
$ git log --pretty=oneline 4d8ecbd409d773fec47da33b7e6c8db0b51487fd..429a06039d185149f387a65e3503b0693ce6d24e
429a06039d185149f387a65e3503b0693ce6d24e (HEAD -> master, origin/master, origin/HEAD) Parallel fetching of available versions (#2280)
6705b085b9bf4754a4c8002a070f436f115dc4d1 Retry on all SocketExceptions (#2254)
a1820273b9f3c7bb5a13d26cd14d30d5bab187ae Use a unqiue file name for the snapshot during testing. (#2303)
72686563e767f8a359e48a267a2c323953a6a0ef Include osx and windows testing on Travis (#2299)
a7a66821d13920b9b22cc394dfa55c679e971e40 Fail travis for lints and warnings (#2301)
25aa24c023453f064dad8f3cce1bbd55269d0efa Omit languageVersion when there is no SDK constraint (#2300)
82e60a3dcb3afe753563e7d304827fb650bc4833 Use LOCALAPPDATA for system cache on windows (#2297)
ceaa86f2c7eb35f044b4c202268a17361de68d13 Enforce and fix lints from package:pedantic (#2291)
6ce1606564352c305bd0f6d97704f0f7f6ebbca0 Use more collection literals for args (#2293)
be245e6baeebb71aaf3b3a260fcfbbb011a9a7e0 Rename some test utilities from Mock to Fake (#2294)
f7638ce85298df7d9e73d717dd4d81f499681720 Refactor Set.add following !Set.contains (#2295)
390022b24bc076cb934385936ac7904f045a75ba Filter out `null` from `getCachedPackages`. (#2292)
0eea0c4421ed0b83c8597b62dacf68b93de172b9 Fix existing hints and lints (#2290)
7cf2fe860a40517ccb65f5efdda9e4dc350142c3 promote strict deps failures to errors from warnings (#2289)
```

Change-Id: I62782b29e16092114940df00811bfdd20c8045fa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/131839
Reviewed-by: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>

CHANGELOG.md

@@ -50,10 +50,31 @@ The Linter was updated to `0.1.109`, which includes:
 
 #### Pub
 
+* `pub get` and `pub upgrade` now fetches version information about hosted
+  dependencies in parallel, improving the time package resolution performance.
+
 * `pub get` and `pub upgrade` no longer precompiles executables from
   dependencies by default. Instead they are precompiled on first `pub run`.
   Use `pub get --precompile` to get the previous behavior.
 
+* Fixed missing retries of DNS failures during `pub get`.
+
+* Importing packages not in `pubspec.yaml` now causes `pub publish` to reject
+  the package.
+
+* Relative paths in `pubspec.lock` are now using `/` also on Windows to make
+  the file sharable between machines.
+
+* Fixed language version in [`.dart_tool/package_config.json`](https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/package-config-file-v2.md)
+  for packages without an explicit sdk constraint.
+
+  Now writes an empty language-version while efore the language version of the
+  current sdk would be used.
+
+* `%LOCALAPPDATA%` is now preferred over `%APPDATA%` when creating a pub cache
+  directory on Windows. `%LOCALAPPDATA%` is not copied when users roam between
+  devices.
+
 #### dart2js
 
 A new representation of runtime types was enabled by default.

DEPS

@@ -119,7 +119,7 @@ vars = {
   "ply_rev": "604b32590ffad5cbb82e4afef1d305512d06ae93",
   "pool_tag": "1.3.6",
   "protobuf_rev": "3746c8fd3f2b0147623a8e3db89c3ff4330de760",
-  "pub_rev": "4d8ecbd409d773fec47da33b7e6c8db0b51487fd",
+  "pub_rev": "429a06039d185149f387a65e3503b0693ce6d24e",
   "pub_semver_tag": "1.4.2",
   "quiver-dart_tag": "2.0.0+1",
   "resource_rev": "f8e37558a1c4f54550aa463b88a6a831e3e33cd6",