use built in travis caching

make sure bundle update is run so that the latest gems are used

.travis.yml

@@ -16,6 +16,8 @@ services:
 
 sudo: false
 
+cache: bundler
+
 env:
   matrix:
     - DEVISE_ORM=mongoid
@@ -23,6 +25,8 @@ env:
 
 before_install: "rm ${BUNDLE_GEMFILE}.lock"
 
+before_script: "bundle update"
+
 script: "bundle exec rake test"
 
 notifications: