Use correct URL for travis status badge

This uses the `devel` branch when displaying the travis-ci status badge.

README.md

 [![PyPI version](https://badge.fury.io/py/ansible.png)](http://badge.fury.io/py/ansible)
 [![PyPI downloads](https://pypip.in/d/ansible/badge.png)](https://pypi.python.org/pypi/ansible)
-[![Build Status](https://travis-ci.org/ansible/ansible.svg?branch=tox_and_travis)](https://travis-ci.org/ansible/ansible)
+[![Build Status](https://travis-ci.org/ansible/ansible.svg?branch=devel)](https://travis-ci.org/ansible/ansible)
 
 
 Ansible