Updating Travis CI build parameters to resolve 1.9.3 build issues and include newer ruby versions.

.travis.yml

@@ -3,9 +3,13 @@ rvm:
   - 1.9.3
   - 1.9.3
   - 2.0.0
   - 2.0.0
   - 2.1.0
   - 2.1.0
+  - 2.2.0
+  - 2.3.0
   - ruby-head
   - ruby-head
   - jruby-19mode
   - jruby-19mode
   - rbx
   - rbx
+before_install:
+  - gem install bundler # the default bundler version on travis is very old and causes 1.9.3 build issues
 matrix:
 matrix:
   allow_failures:
   allow_failures:
     - rvm: ruby-head
     - rvm: ruby-head