location: Use translated reason string

Gio now has API to look up localized strings from desktop files,
so we can display a correctly translated reason where available.

https://bugzilla.gnome.org/show_bug.cgi?id=779413

js/ui/status/location.js

@@ -321,7 +321,7 @@ var AppAuthorizer = new Lang.Class({
     _userAuthorizeApp: function() {
         let name = this._app.get_name();
         let appInfo = this._app.get_app_info();
-        let reason = appInfo.get_string("X-Geoclue-Reason");
+        let reason = appInfo.get_locale_string("X-Geoclue-Reason");
 
         this._showAppAuthDialog(name, reason);
     },