Dependencies URLs in Package.swift should end in .git

[Frizlab]

More info in this PR.

Another reason why this should be done: the actual canonical URL of the git repository does have the .git extension (when copied from GitHub UI).

[stephencelis]

@Frizlab While we are open to discussing such a change, this seems more like a behavior that could be fixed upstream in SPM, and attempting to instead tell every package in the entire ecosystem to follow a convention seems like a tall order.

That said, I don't think anyone would consider this a library bug, so I'm going to convert to a discussion.

[Frizlab]

Noted.
I have added another argument as to why the switch should be made in the top-post.