http: improved test

Author: ShogunPanda

test/async-hooks/test-graph.http.js

@@ -17,7 +17,7 @@ const server = http.createServer(common.mustCall((req, res) => {
   server.close(common.mustCall());
 }));
 server.listen(0, common.mustCall(() => {
-  const req = http.get({
+  http.get({
     host: '::1',
     family: 6,
     port: server.address().port