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
Be valid .travis.yml
Merge pull request #260 from sanemat/feature/ruby-2-0-0

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