Update Num stub for typed_ast 2.7 (#1430)

Field `n` should be a `Union[int, float, complex]`, not just `Union[int, float]`

Author: ilinum

third_party/3/typed_ast/ast27.pyi

@@ -242,7 +242,7 @@ class Repr(expr):
     value = ...  # type: expr
 
 class Num(expr):
-    n = ...  # type: Union[int, float]
+    n = ...  # type: Union[int, float, complex]
 
 class Str(expr):
     s = ...  # type: bytes