Expose didCloseWithCode in RCTReconnectingWebSocket

Summary: Expose didCloseWithCode in RCTReconnectingWebSocket in order to get notified when the reconnecting websocket is closed by the end-point.

Reviewed By: javache

Differential Revision: D5573394

fbshipit-source-id: 78bffeb98c6bf32b059194fc07ffc1f0a7bf4aae

Libraries/WebSocket/RCTWebSocketObserver.m

@@ -61,6 +61,10 @@
   }
 }
 
+- (void)webSocket:(RCTSRWebSocket *)webSocket didCloseWithCode:(NSInteger)code reason:(NSString *)reason wasClean:(BOOL)wasClean
+{
+}
+
 @end
 
 #endif