fix(Connection): swallow all the ws errors after connection's closed (#2077)

Since ws is closing asynchronously and can yield errors while closing,
we should keep swallowing ws errors after the `ws.close()` method
is called.

lib/Connection.js

@@ -132,6 +132,8 @@ class Connection extends EventEmitter {
       this._closeCallback = null;
     }
     this._transport.removeAllListeners();
+    // If transport throws any error at this point of time, we don't care and should swallow it.
+    this._transport.on('error', () => {});
     for (const callback of this._callbacks.values())
       callback.reject(rewriteError(callback.error, `Protocol error (${callback.method}): Target closed.`));
     this._callbacks.clear();