binstubs so that there's no need to write bundle exec bin

.travis.yml

@@ -1,6 +1,9 @@
-before_install: gem install bundler
-before_script: "cd test_app && bundle install && ./script/rails generate impressionist -f && bundle exec rake db:migrate && cd .."
 language: ruby
+
+bundler_args: '--binstubs --without documentation'
+before_install: gem install bundler
+before_script: "cd test_app && bundle install && ./script/rails generate impressionist -f && rake db:migrate && cd .."
+
 rvm:
   - rbx-18mode
   - rbx-19mode