Fixed it! Gist clone URLs don't include the username for some weird
reason? Anyway, it works now. Tested with:
go get go-gist.appspot.com/ImJasonH/7791518
Support /UserName/12345 as well as just /12345 since the username isn't actually used
Merge branch 'master' of https://github.com/ImJasonH/go-gist