also add AsyncGenerator to collections and collections.abc

Author: JelleZijlstra

stdlib/3/collections/__init__.pyi

@@ -35,6 +35,8 @@ from typing import (
     MutableSet as MutableSet,
     AbstractSet as Set,
 )
+if sys.version_info >= (3, 6):
+    from typing import AsyncGenerator as AsyncGenerator
 
 _T = TypeVar('_T')
 _KT = TypeVar('_KT')

stdlib/3/collections/abc.pyi

@@ -35,4 +35,5 @@ if sys.version_info >= (3, 5):
 if sys.version_info >= (3, 6):
     from . import (
         Reversible as Reversible,
+        AsyncGenerator as AsyncGenerator,
     )