Travis ci

Hi again Rahul,

While testing the `/stories/single` change, I've also added Travis CI support that you might decide to use.

Here's a sample passing build with both the `/stories/single` and this branch merged together: https://travis-ci.org/pypt/MediaCloud-API-Client/builds/44620584

Please note that the Travis CI configuration (`.travis.yml`) uses your Media Cloud API key (for the encrypted value, see `env/global/secure/` entry in `.travis.yml`). If you merge this pull request, and on every API key change, you'll need to encrypt it by running:

    gem install travis
    travis encrypt MC_API_KEY=your_key

...and put the new value to `.travis.yml`.