[security] Use crypto.randomBytes() to generate the masking key (#994)

Author: sgress454

lib/Sender.js

@@ -6,6 +6,7 @@
 
 var events = require('events')
   , util = require('util')
+  , crypto = require('crypto')
   , EventEmitter = events.EventEmitter
   , ErrorCodes = require('./ErrorCodes')
   , bufferUtil = require('./BufferUtil').BufferUtil
@@ -315,10 +316,5 @@ function getArrayBuffer(data) {
 }
 
 function getRandomMask() {
-  return new Buffer([
-    ~~(Math.random() * 255),
-    ~~(Math.random() * 255),
-    ~~(Math.random() * 255),
-    ~~(Math.random() * 255)
-  ]);
+  return crypto.randomBytes(4);
 }