Update build badge style

Author: davesque

README.rst

@@ -4,7 +4,7 @@ Simple JWT
 A JSON Web Token authentication plugin for the `Django REST Framework
 <http://www.django-rest-framework.org/>`__.
 
-.. image:: https://circleci.com/gh/davesque/django-rest-framework-simplejwt.svg?style=svg
+.. image:: https://circleci.com/gh/davesque/django-rest-framework-simplejwt.svg?style=shield
   :target: https://circleci.com/gh/davesque/django-rest-framework-simplejwt
 .. image:: https://codecov.io/gh/davesque/django-rest-framework-simplejwt/branch/master/graph/badge.svg
   :target: https://codecov.io/gh/davesque/django-rest-framework-simplejwt