[Mingw-cross-env-list] GitHub team member status for me (@TimothyGu)

[Timothy Gu]

Hi all,

I have used and contributed to MXE for quite some time now, and I am the [5th biggest contributor counted by commits](https://github.com/mxe/mxe/graphs/contributors). I feel that I have a fairly good grasp on the codebase and can be depended upon for this project.

Giving me the permission to push to the official repo can really speed up the process of pushing some trivial patches sent to this project or merging some pull requests, especially when most developers are busy.

Thanks,
Timothy

P.S. you can also comment about this on GitHub as ticket 366: https://github.com/mxe/mxe/issues/366