fix: return null from FitBounds component

mapper/src/App.js

@@ -147,6 +147,8 @@ function FitBounds({ coords, mapState, end, duration, loading }) {
             isInitialLoad.current = false;
         }
     }, [coords, loading, map]); // Dependencies: run when data is ready.
+
+    return null;
 }
 
 function Map({end, duration, slider, mapState, setMapState}) {