Do not test branches other than master

.travis.yml

@@ -1,13 +1,21 @@
 language: ruby
+
 before_install:
   - sudo apt-get update -qq
   - sudo apt-get install -qq -y bsdtar
   - rvm @global do gem uninstall bundler --all --executables
   - gem uninstall bundler --all --executables
   - gem install bundler --version '< 1.7.0'
+
 rvm:
   - 2.0.0
+
+branches:
+  only:
+    - master
+
 env:
   global:
     - NOKOGIRI_USE_SYSTEM_LIBRARIES=true
+
 script: rake test:unit