Use HTTPS URL for submodule to allow read access for non GH users

[Johennes]

This is required to be able to clone the repository and its submodules without having a GitHub account. An example use case is consuming card.io through carthage to build an iOS application within a large team of engineers where people simply cannot be required to sign up for GitHub and upload their SSH key just to build the app.

See also Carthage/Carthage#1865

[josharian]

Thanks for the pull request. This has been discussed fairly extensively in the past, but my search fu is failing me. There are benefits to both ssh and https. If you need https, you can use git's insteadof support: https://stackoverflow.com/questions/1722807/git-convert-git-urls-to-http-urls.

[Johennes]

Thanks for the pointer. So putting this into my global .gitconfig

[url "https://github.com/card-io/card.io-dmz.git"]
    insteadOf = git@github.com:card-io/card.io-dmz.git

indeed makes card.io work with carthage. I still think it would be nice if no additional setup was required just for consuming the framework but I'm fine with this if SSH brings benefits in other use cases. :)