Adds a prereleaser hook for zest.releaser to update the VERSION variable in setup.py. This used to work out of the box but we changed it from 'version' to 'VERSION' and now it no longer works.  I need to submit an upstream fix to zest.releaser to make this case-insensitive. This works in the meantime.
Merge branch 'master' of github.com:astropy/astropy