Add AMD export

FileSaver.js

@@ -244,4 +244,10 @@ var saveAs = saveAs
 // while `this` is nsIContentFrameMessageManager
 // with an attribute `content` that corresponds to the window
 
-if (typeof module !== "undefined") module.exports = saveAs;
+if (typeof module !== "undefined" && module !== null) {
+  module.exports = saveAs;
+} else if ((typeof define !== "undefined" && define !== null) && (define.amd != null)) {
+  define([], function() {
+    return saveAs;
+  });
+}