Travis CI added to Continuous Testing recipe

All set! 
```
question  Continuous testing?
          1)  None
          2)  Guard
          3)  Travis CI
          4)  Guard with Travis CI
       setup  Enter your selection: 
```

I tested both options and it works as expected.
Let me know if you'd like me to make any changes.

I added some Travis documentation links in the .travis.yml file, but if you don't think they belong there I can pull them out. Figured they'd be helpful.