lib: chenged anonymous function to arrow function

Author: taishikato

lib/_http_client.js

@@ -306,7 +306,7 @@ ClientRequest.prototype.abort = function abort() {
   if (this.res) {
     this.res._dump();
   } else {
-    this.once('response', function(res) {
+    this.once('response', (res) => {
       res._dump();
     });
   }