Added weight to MapTypeStyler

As described here: https://developers.google.com/maps/documentation/javascript/styling

googlemaps/google.maps.d.ts

@@ -1338,6 +1338,7 @@ declare module google.maps {
         lightness?: number;
         saturation?: number;
         visibility?: string;
+        weight?: number;
     }
 
     /***** Layers *****/