Update the version of django-reversion to 1.8.7.
Update the version of django-reversion to 1.8.7.

According to the django-reversion docs, this the version
compatible with django 1.7+

https://django-reversion.readthedocs.org/en/latest/django-versions.html

alphagov/stagecraft,alphagov/stagecraft,alphagov/stagecraft,alphagov/stagecraft