bundler pre is faster, so use it again

.travis.yml

@@ -11,6 +11,7 @@ env:
   - DB=postgres BUILD_TYPE=other
   - DB=mysql BUILD_TYPE=other
 
+before_install: gem install bundler --pre
 bundler_args: "--without development production"
 before_script: "./config/ci/before-travis.sh"
 script: "bundle exec rake travis"