fix NamedAgg aggfunc should be AggScalar (#128)

Author: bschnurr

pandas/core/groupby/generic.pyi

@@ -12,12 +12,11 @@ if sys.version_info >= (3, 8):
 else:
     from typing_extensions import Literal
 
-class NamedAgg(NamedTuple):
-    column: str = ...
-    aggfunc: AggFuncType = ...
-
 AggScalar = Union[str, Callable[..., Any]]
 ScalarResult = ...
+class NamedAgg(NamedTuple):
+    column: str = ...
+    aggfunc: AggScalar = ...
 
 def generate_property(name: str, klass: Type[FrameOrSeries]) : ...
 def pin_whitelisted_properties(klass: Type[FrameOrSeries], whitelist: FrozenSet[str]) : ...