Use bundler to execute test

.travis.yml

@@ -9,7 +9,7 @@ env:
   - RAILS_VERSION="~>4.0.0"
   - RAILS_VERSION="~>4.1.0"
   - RAILS_VERSION="~>4.2.0"
-script: "rake spec:all"
+script: "bundle exec rake spec:all"
 before_install:
  - sudo apt-get update
  - sudo apt-get install idn