Support Git URLs with semver tags

When a dependency is a Git URL that contains a valid semver tag, then
check-dependencies will also run its checks.

* The tag is also considered valid when prefixed with 'v' as it is common
pratice.
* Updated tests (ok and not ok) and added others specific to git urls
* Dont ignore node_modules in fixtures because we need them for the tests

Closes #4
Update npm deps