using path + version in dependency should cause error since version is not used

[timotheecour]

cd path/to/GtkD git branch shows no dev branch yet:

"gtk-d": {"path": "path/to/GtkD", "version": "~dev",},

doesn't complain; we shoul error instead of silently accepting this (until dub honors version branch, that is)

[Geod24]

Found this when implementing the parser. It would be fairly trivial to deprecate but IIRC it wasn't rare: https://github.com/dlang/dub/blob/56077da3a269299ab661215d0112364052deab6a/source/dub/recipe/packagerecipe.d#L356-L360