docs: improve readme receiver example (#309)

Signed-off-by: Grant Timmerman <timmerman+devrel@google.com>

README.md

@@ -34,14 +34,14 @@ You can choose almost any popular web framework for port binding. Use an
 binary and structured events in either the 1.0 or 0.3 protocol formats.
 
 ```js
-const {
-  CloudEvent,
-  Receiver
-} = require("cloudevents");
+const app = require("express")();
+const {Receiver} = require("cloudevents");
 
+app.post("/", (req, res) => {
   // body and headers come from an incoming HTTP request, e.g. express.js
   const receivedEvent = Receiver.accept(req.headers, req.body);
   console.log(receivedEvent);
+});
 ```
 
 #### Emitting Events

examples/express-ex/index.js

@@ -4,7 +4,6 @@ const express = require("express");
 const {Receiver} = require("cloudevents");
 
 const app = express();
-const receiver = new Receiver();
 
 app.use((req, res, next) => {
   let data = "";
@@ -20,7 +19,7 @@ app.use((req, res, next) => {
   });
 });
 
-app.post("/", function (req, res) {
+app.post("/", (req, res) => {
   console.log("HEADERS", req.headers);
   console.log("BODY", req.body);
 
@@ -34,6 +33,6 @@ app.post("/", function (req, res) {
   }
 });
 
-app.listen(3000, function () {
+app.listen(3000, () => {
   console.log("Example app listening on port 3000!");
 });