The fact that the Github license allow forking does not mean all sources their are free to copy and use.
Github's response to this question (2013 already):
Pavlo Mykhalov @growtofill 13 Jul 2013
What license terms are applicable to a public @github project if none are specified within the project?
GitHub Support
@GitHubHelp
You should ask the owner to apply an open source license if you want to use it.
7:32 PM - 13 Jul 2013Replying to @growtofill @growtofill We don’t impose any licenses on repositories.
Thank you very much for your support and this information from github's support team. I appreciate it. Do you have a link to this quote or question/answer?
Sure, here's the twitter link:
Thanks a lot for this! :]