fix(themeable-browser): allow hidden and clear cache

it wrong from boolean to string, after 1 year i update it

src/@ionic-native/plugins/themeable-browser/index.ts

@@ -48,9 +48,9 @@ export interface ThemeableBrowserOptions {
 
   // inAppBrowser options
   location?: string;
-  hidden?: string;
-  clearcache?: string;
-  clearsessioncache?: string;
+  hidden?: boolean;
+  clearcache?: boolean;
+  clearsessioncache?: boolean;
   zoom?: string;
   hardwareback?: string;
   mediaPlaybackRequiresUserAction?: string;