Bumped pub revision

Change-Id: I8ca3203423a98f8a0b02f0f8b458623025f1ddd6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149847
Auto-Submit: Jonas Jensen <jonasfj@google.com>
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>

CHANGELOG.md

@@ -87,6 +87,10 @@ Updated the Linter to `0.1.116`, which includes:
 ### Dart VM
 
 ### Pub
+* `pub run` and `pub global run` accepts a `--enable-experiment` flag enabling
+  experiments in the Dart VM (and language).
+* Publishing Flutter plugins using the old plugin format is no longer allowed.
+  Plugins using the old plugin format can still be consumed.
 * Introduce `pub outdated --mode=null-safety` that will report which of your
   dependencies you can upgrade to fully support null safety.
 * Fix `pub run` precompilation with relative `PUB_CACHE` paths (#2486)

DEPS

@@ -127,7 +127,7 @@ vars = {
   "ply_rev": "604b32590ffad5cbb82e4afef1d305512d06ae93",
   "pool_rev": "86fbb2cde9bbc66c8d159909d2f65a5981ea5b50",
   "protobuf_rev": "3746c8fd3f2b0147623a8e3db89c3ff4330de760",
-  "pub_rev": "a4bc2dd08630f85a94f506eab037fcaaedb42222",
+  "pub_rev": "6178cdf284baf2345d1ea578b7176a754aa576fe",
   "pub_semver_tag": "v1.4.4",
   "quiver-dart_tag": "2.0.0+1",
   "resource_rev": "f8e37558a1c4f54550aa463b88a6a831e3e33cd6",