Improve type annotation of Map.__init__

Author: hukkinj1

immutables/_map.pyi

@@ -41,9 +41,12 @@ class MapItems(Generic[K, V]):
 
 
 class Map(Mapping[K, V]):
+    @overload
+    def __init__(self, **kw: V) -> None: ...
+    @overload
     def __init__(
-        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]] = ..., **kw: V
-    ): ...
+        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]], **kw: V
+    ) -> None: ...
     def __reduce__(self) -> Tuple[Type[Map], Tuple[dict]]: ...
     def __len__(self) -> int: ...
     def __eq__(self, other: Any) -> bool: ...