Add Ruby2.0.0 build in Travis-ci, and allowed to fail

http://about.travis-ci.org/docs/user/build-configuration/#Rows-That-are-Allowed-To-Fail

.travis.yml

@@ -3,6 +3,7 @@ rvm:
   - 1.8.7
   - 1.9.2
   - 1.9.3
+  - 2.0.0
   - jruby
   - ree
 script: "bundle exec rake spec:all"
@@ -15,3 +16,6 @@ notifications:
       - sbazyl@google.com
     on_success: change
     on_failure: change
+matrix:
+  allow_failures:
+    - rvm: 2.0.0