update github3.py to 1.0.0a4
update github3.py to 1.0.0a4

Needed to pickup @frossie's fix for annotated tag generation:

    https://github.com/sigmavirus24/github3.py/commit/c8e3588846e6b69c4e9160a7808ad393c549105f

lsst-sqre/sqre-codekit,lsst-sqre/sqre-codekit