Use strict mode for function scopes.

Global strict mode is problematic when the script is concatenated
with non-strict scripts.

.jshintrc

@@ -23,7 +23,7 @@
     "devel"         : true,
 
     "strict"        : true,
-    "globalstrict"  : true,
+    "globalstrict"  : false,
 
     "asi"           : false,
     "laxbreak"      : false,

src/perfect-scrollbar.js

@@ -1,8 +1,9 @@
 /* Copyright (c) 2012 HyeonJe Jun (http://github.com/noraesae)
  * Licensed under the MIT License
  */
-'use strict';
 (function (factory) {
+  'use strict';
+
   if (typeof define === 'function' && define.amd) {
     // AMD. Register as an anonymous module.
     define(['jquery'], factory);
@@ -14,6 +15,7 @@
     factory(jQuery);
   }
 }(function ($) {
+  'use strict';
 
   // The default settings for the plugin
   var defaultSettings = {