Add Ruby v2.0.0 to Travis CI Builds

Installed Ruby 2.0.0 locally. All tests pass.

```
[jm@rawr capistrano (travis-ruby-2.0)]$ ruby -v
ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-darwin12.2.1]
[jm@rawr capistrano (travis-ruby-2.0)]$ rake test
/usr/local/opt/rbenv/versions/2.0.0-p0/bin/ruby -I"lib:lib:test" -I"/usr/local/opt/rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/rake-10.0.3/lib" "/usr/local/opt/rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/rake-10.0.3/lib/rake/rake_test_loader.rb" "test/**/*_test.rb" 
Run options: 

# Running tests:

Finished tests in 0.546737s, 1090.1037 tests/s, 2690.5075 assertions/s.                                       
596 tests, 1471 assertions, 0 failures, 0 errors, 0 skips

ruby -v: ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-darwin12.2.1]
```