Update g.json

The git plugin won't download for me any more. Github doesn't appear to redirect the old repository for codeload download.

https://github.com/kemayo/sublime-text-2-git will redirect fine but https://codeload.github.com/kemayo/sublime-text-2-git/zip/master (which is what's used) gives a 500.
Merge pull request #1846 from petehamilton/patch-1

Update sublime-git package download location