Fix error with set_cookie() during tests

According to https://github.com/pallets/werkzeug/blob/f3c803b3ade485a45f12b6d6617595350c0f03e2/CHANGES.rst#version-230
The first positional server_name parameter to set_cookie and delete_cookie is deprecated. Use the domain parameter instead."

website/frontend/views_test.py

@@ -26,7 +26,7 @@ def test_quick_start(self):
     def test_home_page_french_cookie(self):
         "Test / in french (cookie)"
         server_name = self.app.config.get('SERVER_NAME') or 'localhost'
-        self.client.set_cookie(server_name, 'language', 'fr')
+        self.client.set_cookie('language', 'fr', domain=server_name)
         response = self.client.get("/")
         self.assert200(response)
         self.assertIn(b'fichiers audio', response.data)