[fix] Remove existing points from map in appenData before calling render

Remove the existing points from the map in appendData
before calling the render method. Otherwise,
the original points are duplicated on the map.

src/js/netjsongraph.render.js

@@ -654,6 +654,9 @@ class NetJSONGraphRender {
         features: self.data.features.concat(JSONData.features),
       };
 
+      // Remove the existing points from the map. Otherwise,
+      // the original points are duplicated on the map.
+      self.leaflet.geoJSON.removeFrom(self.leaflet);
       self.utils.render();
     }