Adding @matthew-brett to maintainers so he can make a release

[choldgraf]

I've added @matthew-brett as a maintainer for this project, in the hopes he might be willing to help with releases from time to time.

@matthew-brett , I believe that these are the instructions that you need to follow to make a release. You should now have all the permissions needed to do so. Want to give it a shot?

https://compass.executablebooks.org/en/latest/development/conventions.html#the-process-of-creating-a-release