updated serializer.show() in matplotserializer python interface

Fixed #20 (closed) .

plot_serializer/matplotlib/serializer.pyi

@@ -46,3 +46,4 @@ class MatplotlibSerializer(Serializer):
         gridspec_kw: Optional[Dict[str, Any]] = None,
         **fig_kw: Any,
     ) -> Tuple[MplFigure, Any]: ...
+    def show(self, *, block: Optional[bool] = None) -> None: ...