Adding Travis CI badge to docs
Adding Travis CI badge to docs

Includes:
* Updating PyPI badges to be .svg

WGBH/django-versatileimagefield,WGBH/django-versatileimagefield,theskumar/django-versatileimagefield,theskumar/django-versatileimagefield,WGBH/django-versatileimagefield,respondcreate/django-versatileimagefield,respondcreate/django-versatileimagefield,respondcreate/django-versatileimagefield,theskumar/django-versatileimagefield