chore(build): temporarily deactivate dev build for Dart

Please revert when angular#2798 is closed!

Author: tbosch

.travis.yml

@@ -24,7 +24,10 @@ env:
  matrix:
  - MODE=js DART_CHANNEL=dev
  - MODE=dart DART_CHANNEL=stable
- - MODE=dart DART_CHANNEL=dev
+ # Deactivate dev mode for Dart as there are breaking changes.
+ # Reactivate when https://github.com/angular/angular/issues/2798 is fixed!
+ # (Note: we need the dev channel as Google3 is close to it and ahead of stable channel)
+ # - MODE=dart DART_CHANNEL=dev
 
 addons:
  firefox: "38.0"