Typing: Narrow down types of arguments (NDFrame) #10
[Typing: Narrow down types of arguments (NDFrame) #10](https://github.com/noatamir/pydata-workshop/issues/10)
Made these specifications to Literals:
- [ X] Specify date_unit in to_json more precisely
- [ X] Specify mode in to_hdf more precisely
- [ X] Specify complib in to_hdf more precisely
- [ X] Specify format in to_hdf more precisely

@phofl @jorisvandenbossche @noatamir @MarcoGorelli 
Thanks for the PR @mKlepsch! The CI caught some errors which I think you can solve locally if you run pre-commit. Let us know if you need help.  Hope it works now! Hi, I can't figure out why it is still failing the CI. Could you give me some pointers? you'll need to run the pre-commit hooks, please check the contributing guide for how to do that You can do:

```
pre-commit install
pre-commit run --all-files
```

(It's probably a space at the end of the line, which is disallowed

 Thanks @mKlepsch 