add: working reset zoom

app/lib/widgets/choropleth_map.dart

@@ -40,7 +40,7 @@ class ChoroplethMapState extends State<ChoroplethMap> {
 
   void resetZoom() {
     setState(() {
-      _choroplethMapKey.currentState?.resetZoom();
+      _zoomPanBehavior.zoomLevel = 1;
     });
   }