Various fixes for gh clone

1. When you run `gh clone git://github.com/jingweno/gh gh`, `gh` would transform it into `git clone git://github.com/jingweno/gh git://github.com/tgkokk/gh`. In other words, it wouldn't stop if it found a URL. I fixed it.
2. I added noop. (not really a fix)
3. Now, if `gh clone foo bar` is run, `git clone git@github.com:tgkokk/foo bar` is run. It's what `hub` also does, you can check with `hub --noop`.