Fix missing argument (gramps-project/gramps-web#212

Author: DavidMStraub

gramps_webapi/api/resources/exporters.py

@@ -186,7 +186,7 @@ def get(self, args: Dict, extension: str) -> Response:
 class ExporterFileResultResource(ProtectedResource, GrampsJSONEncoder):
     """Export file result resource."""
 
-    def get(self, filename: str) -> Response:
+    def get(self, extension: str, filename: str) -> Response:
         """Get the processed file."""
         export_path = current_app.config.get("EXPORT_DIR")