Add a missing field to show it in toString()

Change-Id: Ie2d4a2c37319fe60914d8e8a270f6b420e8df06e

@@ -67,6 +67,7 @@ public class LambdaResourceRequest implements ResourceRequest {
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(this)
+                .add("lambda", lambda)
                 .toString();
     }
 }