Cap pub's barback constraint below 0.14.1.

sdk/lib/_internal/pub/lib/src/barback.dart

Index: sdk/lib/_internal/pub/lib/src/barback.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback.dart b/sdk/lib/_internal/pub/lib/src/barback.dart
index 83b63de92b8f8cbc582889014261b7e1be6908fe..d0f11f7ea9feae016e73f4ba26524e70c85dd21f 100644
--- a/sdk/lib/_internal/pub/lib/src/barback.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback.dart
@@ -34,7 +34,7 @@ import 'version.dart';
 /// constraint and barback's version.
 ///
 /// [compat]: https://gist.github.com/nex3/10942218
-final supportedVersions = new VersionConstraint.parse(">=0.13.0 <0.14.2");
+final supportedVersions = new VersionConstraint.parse(">=0.13.0 <0.14.1");
 
 /// A list of the names of all built-in transformers that pub exposes.
 const _BUILT_IN_TRANSFORMERS = const ['\$dart2js'];