Tell Travis to fast-finish our builds

This will make Travis not waiting for all builds to finish before notify
us the build result.

http://blog.travis-ci.com/2013-11-27-fast-finishing-builds/

.travis.yml

@@ -20,6 +20,7 @@ gemfile:
   - gemfiles/4.1.gemfile
 
 matrix:
+  fast_finish: true
   allow_failures:
     - rvm: jruby-19mode
     - rvm: rbx-19mode