Add osx build env

.travis.yml

@@ -3,16 +3,16 @@ bundler_args: --without development
 rvm:
   - ruby-head
   - 2.2
-  - 2.1.1
-  - 2.1.0
-  - 2.0.0
+  - 2.1
+  - 2.0
   - 1.9.3
-  - jruby-19mode
+os:
+  - linux
+  - osx
 matrix:
   fast_finish: true
   allow_failures:
     - rvm: ruby-head
-    - rvm: jruby-19mode
 env: TEST=true
 before_install: git submodule update --init --recursive
 script: bundle exec rake test