Support go get gogs.io/gogs

[fgm]

Currently, the code is hosted on https://github.com/gogs/gogs, which couples gogs to this hosting solution, although the canonical project URL is gogs.io, which appears to be a Peach instance using this configuration.

It would be better in the longer term for Gogs to use its gogs.io custom domain as a canonical import, as it would break the dependency on github, just in case it became necessary to change. Then one could just do a go get -u gogs.io/gogs and get the code from whatever forge the project happens to be hosted on, possibly including a Gogs instance at some point.