Use RVM in Go build

.travis.yml

@@ -4,7 +4,11 @@ go:
 install:
   - script/bootstrap
   - export PATH="$HOME/gopath/bin:$PATH"
-  - ruby -v
+  - rvm use 2.1.0 --install --binary --fuzzy
+  - export BUNDLE_GEMFILE=$PWD/Gemfile
+  - ruby --version
+  - rvm --version
+  - gem --version
   - script/cached-bundle install --deployment --without development
 script:
   - script/build