The FloatingActionButton requires an icon (#1293)

diff --git a/packages/google_maps_flutter/README.md b/packages/google_maps_flutter/README.md
index dc37bd8..b4a8465 100644
--- a/packages/google_maps_flutter/README.md
+++ b/packages/google_maps_flutter/README.md
@@ -139,6 +139,7 @@
       floatingActionButton: FloatingActionButton.extended(
         onPressed: _goToTheLake,
         label: Text('To the lake!'),
+        icon: Icon(Icons.directions_boat),
       ),
     );
   }