added ruby 2.1.3 in the ci rubies to test the project on

by the way, there are 2 tests failing and I suggest enabling trevis ci for your repository.

```
rspec ./spec/integration/request_spec.rb:13 # RestClient::Request ssl verification is successful with the correct ca_file
rspec ./spec/integration/request_spec.rb:23 # RestClient::Request ssl verification is successful with the correct ca_path
```