Use Buffer.from in place of new Buffer

Node has [deprecated](https://nodejs.org/api/buffer.html#buffer_class_buffer) the use of `new Buffer()` as of v6.0.0 and has assigned it a stability score of 0. The Javascript tutorial should utilize [`Buffer.from`](https://nodejs.org/api/buffer.html#buffer_class_method_buffer_from_str_encoding) instead, which was introduced in v5.10.0.

Specifically, the [message sending example](https://www.rabbitmq.com/tutorials/tutorial-one-javascript.html) with this line:

`ch.sendToQueue(q, new Buffer('Hello World!'));`

should be updated to:

`ch.sendToQueue(q, Buffer.from('Hello World!'));`

Author: Robinnnnn

javascript-nodejs/src/send.js

@@ -8,7 +8,7 @@ amqp.connect('amqp://localhost', function(err, conn) {
     var msg = 'Hello World!';
 
     ch.assertQueue(q, {durable: false});
-    ch.sendToQueue(q, new Buffer(msg));
+    ch.sendToQueue(q, Buffer.from(msg));
     console.log(" [x] Sent %s", msg);
   });
   setTimeout(function() { conn.close(); process.exit(0) }, 500);