Add use strict back

Author: wyuenho

Gruntfile.js

@@ -51,7 +51,7 @@ module.exports = function (grunt) {
             '  }\n' +
             '  // Browser\n' +
             '  else factory(this, this._, this.Backbone);\n' +
-            '}(function (root, _, Backbone) {\n\n  ',
+            '}(function (root, _, Backbone) {\n\n  "use strict";\n\n',
           footer: 'return Backgrid;\n' +
             '}));'
         },

lib/backgrid.js

@@ -18,7 +18,9 @@
   else factory(this, this._, this.Backbone);
 }(function (root, _, Backbone) {
 
-  /*
+  "use strict";
+
+/*
   backgrid
   http://github.com/wyuenho/backgrid