Fixing an issue in which the ES6 promise module was erratically included

lib/index.js

@@ -14,22 +14,18 @@
   */
  (function (name, definition) {
     if (typeof define === 'function' && define.amd) {
-        // Exporting the Promise polyfill.
-        this.ES6Promise.polyfill();
         // Defining the module in an AMD fashion.
-        define(['blueimp-md5', 'popsicle', 'proxify-url'], definition);
+        define(['blueimp-md5', 'popsicle', 'proxify-url', 'es6-promise'], definition);
     } else if (typeof module !== 'undefined' && module.exports) {
-        // Exporting the Promise polyfill.
-        require('es6-promise').polyfill();
         // Exporting the module for Node.js/io.js.
         module.exports = definition(
           require('blueimp-md5').md5,
           require('popsicle'),
-          require('proxify-url')
+          require('proxify-url'),
+	  require('es6-promise')  
         );
     } else {
-        this.ES6Promise.polyfill();
-        var instance = definition(this.md5, this.popsicle, this.proxify);
+        var instance = definition(this.md5, this.popsicle, this.proxify, this.ES6Promise);
         var old      = this[name];
 
         /**
@@ -42,8 +38,13 @@
         };
         this[name] = instance;
     }
- })('gravatar', function (md5, popsicle, proxify) {
-
+ })('gravatar', function (md5, popsicle, proxify, es6) {
+
+  /**
+   * Polyfill ES6 Promise.
+   */
+  es6.polyfill();
+
   /**
    * The Gravatar service base URL.
    */