Improve argument regex

Now, I am parsing the argument with this posix regex:

```
(https?://github.com/)([A-Z|a-z|0-9|-]+)(/)([A-Z|a-z|0-9|-]+)(/)?
```


[Debuggex Demo](https://www.debuggex.com/r/8z_J_tLR6aDE5_cN)

Remember that the regex must be posix only because of bash! No perl regex allowed so no `\w` or `\d`.

If you have any idea to improve it feel free to comment.