Adds SublimeGit packages.json url

Not sure if you wanted it at the bottom, or in line with the other
non-github and non-bitbucket urls. Please let me know if i should
move it.

repositories.json

@@ -2,6 +2,7 @@
 	"schema_version": "1.2",
 	"repositories": [
 		"https://github.com/SublimeText",
+		"http://release.sublimegit.net/packages.json",
 		"http://sublime.wbond.net/packages.json",
 		"http://wuub.net/packages.json",
 		"https://bitbucket.org/abraly/zap-gremlins",