Don't leak punycode to global scope

Gruntfile.js

@@ -10,7 +10,7 @@ module.exports = function(grunt) {
             '  Copyright (c) <%= grunt.template.today("yyyy") %> <%= pkg.author.name %>' +
             '\n\n  Released under <%= _.pluck(pkg.licenses, "type").join(", ") %> License\n*/\n',
         pre: '\n(function(window, document, undefined){\n\n',
-        post: '\n})(window, document);'
+        post: '\n}).call({}, window, document);'
     };
 
     // Project configuration.

dist/html2canvas.js

@@ -2835,4 +2835,4 @@ function hasEntries(array) {
     return array.length > 0;
 }
 
-})(window, document);
+}).call({}, window, document);