Update index.ts (#1461)

Author: willum070

samples/advanced-markers-draggable/index.ts

@@ -18,7 +18,7 @@
     const draggableMarker = new google.maps.marker.AdvancedMarkerView({
         map,
         position: {lat: 37.39094933041195, lng: -122.02503913145092},
-        draggable: true,
+        gmpDraggable: true,
         title: "This marker is draggable.",
     });
     // [END maps_advanced_markers_draggable_marker]