collections: Update for underlying module renaming to "ucollections".

collections/collections/__init__.py

@@ -2,7 +2,7 @@
 # Reason:
 # CPython implementation brings in metaclasses and other bloat.
 # This is going to be just import-all for other modules in a namespace package
-from _collections import *
+from ucollections import *
 try:
     from .defaultdict import defaultdict
 except ImportError: