Change WeakDictionary to WeakValueDictionary in a couple more places.
Change WeakDictionary to WeakValueDictionary in a couple more places.

WeakValueDictionary.copy(),
WeakKeyDictionary.copy():  Actually return the copy!

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator