Fix Blueprint inheritence

src/flask/blueprints.py

@@ -76,7 +76,7 @@ def add_url_rule(self, rule, endpoint=None, view_func=None, **options):
         )
 
 
-class Blueprint(_PackageBoundObject):
+class Blueprint(Skeleton):
     """Represents a blueprint, a collection of routes and other
     app-related functions that can be registered on a real application
     later.