fixed typo in assignment id getter

app.py

@@ -65,7 +65,7 @@ with demo:
     def _submit(state, dummy):
         query = parse_qs(dummy[1:])
         assert "assignment_id" in query, "No assignment ID provided, unable to submit"
-        state["assignmentId"] = query["assignment_id"]
+        state["assignment_id"] = query["assignment_id"]
         url = "https://workersandbox.mturk.com/mturk/externalSubmit"
         return requests.post(url, data=state)