tg: fix launching with kajiki after moving to FullStackApplicationConfigurator 27d9ca0c8381

Application start failed with:
    TypeError: 'FullStackApplicationConfigurator' object is not subscriptable

kallithea/config/app_cfg.py

@@ -92,7 +92,7 b' try:'
 except ImportError:
     pass
 else:
-    base_config['renderers'].append('kajiki')
+    base_config.get_blueprint_value('renderers').append('kajiki')
     enable_debugbar(base_config)