Update impress.js

Fixed typo from "how thing work" to "how things work"

Author: bijanbwb

js/impress.js

@@ -19,7 +19,7 @@
 /*jshint bitwise:true, curly:true, eqeqeq:true, forin:true, latedef:true, newcap:true,
          noarg:true, noempty:true, undef:true, strict:true, browser:true */
 
-// You are one of those who like to know how thing work inside?
+// You are one of those who like to know how things work inside?
 // Let me show you the cogs that make impress.js run...
 (function ( document, window ) {
     'use strict';