Fix annotations formatting for plain typing.Callable

The typing.Callable class may be used without generic arguments, in which case it is equivalent to collections.abc.Callable.

tests/typing_test_data.py

@@ -48,7 +48,11 @@ def f8(x: Callable[[int, str], int]) -> None:
     pass
 
 
-def f9(x: Tuple[int, str], y: Tuple[int, ...]) -> None:
+def f9(x: Callable) -> None:
+    pass
+
+
+def f10(x: Tuple[int, str], y: Tuple[int, ...]) -> None:
     pass
 
 
@@ -56,5 +60,6 @@ class CustomAnnotation:
     def __repr__(self):
         return 'CustomAnnotation'
 
-def f10(x: CustomAnnotation(), y: 123) -> None:
+
+def f11(x: CustomAnnotation(), y: 123) -> None:
     pass