add support for github dependencies

[reharik]

Hi I added support for dependencies like "npm-install-missing":"git+https://github.com/AlexCline/npm-install-missing.git"

I have added some tests too that confirm it. When running the test suite I was unable to get 3 of your tests to pass, but I suspect that that may be environmental

I hope you can merge this as I like to reference my modules from github till I'm nice and confident in them , then publish to npm if appropriate. thanks

[reharik]

unfortunately I seem to have failed the ci. but my tests should work. So not sure what's going on. Please let me know if there is anything I need to do.