Run specs on Travis on Ruby 2.1.3 as well as 1.9.3

Also use bundler to run the specs

.travis.yml

@@ -1,11 +1,12 @@
 language: ruby
 rvm:
   - 1.9.3
+  - 2.1.3
 before_install:
   - sh .travis/install_riakcs.sh
 before_script:
   - cp config.yml.example config.yml
-script: rake test
+script: bundle exec rake test
 branches:
   only:
     - master