Change ruby version in .ruby-version

In our ruby-version, the ruby version is set to ``` 2.0.0 ``` (without any patch level).
*rbenv* has strict version matching whereas *rvm* uses pattern matching. e.g. [ruby-]2.0.0[-p247]

It's best to specify the patch level to our ruby version.

Ref: 
http://stackoverflow.com/questions/17589199/how-to-use-any-patchlevel-of-a-ruby-version-with-ruby-version-rbenv-rvm