Test on Chrome on Travis (flutter#16)

Author: kevmoo

.travis.yml

@@ -1,17 +1,24 @@
 language: dart
-sudo: false
+
 dart:
   - dev
   - stable
-cache:
-  directories:
-    - $HOME/.pub-cache
+
 dart_task:
   - test: --platform vm
-  - test: --platform firefox
+  - test: --platform chrome
   - dartanalyzer
   - dartfmt
+
 matrix:
   exclude:
     - dart: dev
       dart_task: dartfmt
+
+# Only building master means that we don't run two builds for each pull request.
+branches:
+  only: [master]
+
+cache:
+  directories:
+    - $HOME/.pub-cache