try fix readme

Author: bckohan

README.rst

@@ -11,7 +11,6 @@
    :target: https://pypi.python.org/pypi/django-enum/
 
 .. |PyPI djversions| image:: https://img.shields.io/pypi/djversions/django-enum.svg
-   :alt: Supported Django versions
    :target: https://pypi.org/project/django-enum/
 
 .. |PyPI status| image:: https://img.shields.io/pypi/status/django-enum.svg