Redesign UMD code to allow imports

lib/chai-as-promised.js

@@ -1,26 +1,24 @@
-(function () {
+(function (factory) {
     "use strict";
-
-    // Module systems magic dance.
-
     /* istanbul ignore else */
     if (typeof require === "function" && typeof exports === "object" && typeof module === "object") {
         // NodeJS
-        module.exports = chaiAsPromised;
+        module.exports = factory();
     } else if (typeof define === "function" && define.amd) {
         // AMD
-        define(function () {
-            return chaiAsPromised;
-        });
+        define(factory);
     } else {
         /*global self: false */
 
         // Other environment (usually <script> tag): plug in to global chai instance directly.
+        var chaiAsPromised = factory();
         chai.use(chaiAsPromised);
 
         // Expose as a property of the global object so that consumers can configure the `transferPromiseness` property.
         self.chaiAsPromised = chaiAsPromised;
     }
+}(function () {
+    "use strict";
 
     chaiAsPromised.transferPromiseness = function (assertion, promise) {
         assertion.then = promise.then.bind(promise);
@@ -371,4 +369,6 @@
             };
         });
     }
-}());
+
+    return chaiAsPromised;
+}));