mk_app does not work with lambda functions

The following simple app does not work:
https://github.com/otosense/plunk/blob/master/plunk/sb/front_experiments/crudify_funcnodes/minimal_lambda_bug.py

Code for the app:
```python
from streamlitfront import mk_app

if __name__ == "__main__":
    app = mk_app([lambda res: res])

    app()
```