fix(app-preferences): fix bug with fetch method

closes #1299

src/@ionic-native/plugins/app-preferences/index.ts

@@ -37,7 +37,6 @@ export class AppPreferences {
    * @return {Promise<any>} Returns a promise
    */
   @Cordova({
-    sync: true,
     callbackOrder: 'reverse'
   })
   fetch(dict: string, key?: string): Promise<any> { return; }