added the enum used in requestFileSystem

cordova/plugins/FileSystem.d.ts

@@ -15,7 +15,7 @@ interface Window {
      * @param errorCallback     A callback that is called when errors happen, or when the request to obtain the filesystem is denied.
      */
     requestFileSystem(
-        type: number,
+        type: LocalFileSystem,
         size: number,
         successCallback: (fileSystem: FileSystem) => void,
         errorCallback?: (fileError: FileError) => void): void;
@@ -371,3 +371,8 @@ interface Cordova {
     }
 }
 
+
+declare enum LocalFileSystem {
+    PERSISTENT=0,
+    TEMPORARY=1
+}