Add GitHub API response to the `Vcs_Reference` instance.    This is intended for use in subclasses, e.g. to change the `downloadUrl` from `zipball_url` to an asset URL.
Add GitHub API response to the `Vcs_Reference` instance. 
 
This is intended for use in subclasses, e.g. to change the `downloadUrl` from `zipball_url` to an asset URL.
YahnisElsts/plugin-update-checker,YahnisElsts/plugin-update-checker