Remove Promise polyfill

tests/mocha/multiple-renders.html

@@ -3,6 +3,7 @@
     <meta charset="utf-8">
     <title>Mocha Tests</title>
     <link rel="stylesheet" href="lib/mocha.css" />
+    <script src="../../node_modules/bluebird/js/browser/bluebird.js"></script>
     <script src="../../dist/html2canvas.js"></script>
     <script src="../assets/jquery-1.6.2.js"></script>
     <script src="lib/expect.js"></script>
@@ -25,7 +26,6 @@
 <div id="green-block"></div>
 <script>mocha.setup('bdd')</script>
 <script>
-    var Promise = html2canvas.Promise;
     describe("Multiple renders", function() {
         it("render correctly", function(done) {
             this.timeout(10000);