Fixed Travis CI link for rails

The previous link for Travis CI for rails in the documentation was broken.

Corrected the broken link and added full path for rails project.

Attaching the image for broken link :- 

![travis-ci](https://f.cloud.github.com/assets/1220255/764027/ff71d7c8-e808-11e2-9e5a-d071f1d2d2af.png)