Update clientCommandMessageReg to allow for command enclosed in backticks

Author: rosslavery

lib/worker.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const utils = require('./utils');
-const clientCommandMessageReg = /ERR unknown command '\s*client\s*'/;
+const clientCommandMessageReg = /ERR unknown command ['`]\s*client\s*['`]/;
 
 module.exports = function(Queue) {
   // IDEA, How to store metadata associated to a worker.