Switch from the GitHub Committer Authorization Strategy to Matrix Auth
Switch from the GitHub Committer Authorization Strategy to Matrix Auth

This should address the issues seen by @lavaliere with #9, and requires at least
a master image of `rtyler/codevalet-master:2017-08-20.1` or later.

:shipit:

Fixes #9

CodeValet/codevalet,CodeValet/codevalet,CodeValet/codevalet