[fix] redirect when saving preferences

Erroneously commit 87e4c4762 droped the 302 redirect.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/webapp.py

@@ -813,7 +813,7 @@ def preferences():
 
     # save preferences
     if request.method == 'POST':
-        resp = make_response(url_for('index', _external=True))
+        resp = make_response(redirect(url_for('index', _external=True)))
         try:
             request.preferences.parse_form(request.form)
         except ValidationException: