(types): add @types/sade, fix transpileOnly default

[agilgur5]

• transpileOnly default being the wrong type was found as a result of
  the better typing

I originally made this as a follow-up to #407 , as prog is passed around as an argument there (and is any without these types), but that hasn't gotten a response in almost a month now 😐 😐
So figured I'd separate it out.

Just as a note, the @types/sade package was reviewed by DT, but never got a response from the maintainer, lukeed/sade#27 (comment)

[agilgur5]

Huh, this test is failing locally too and I'm not totally sure why 🤔 Is 'false' getting evaluated wrong?

[agilgur5]

Yep, looks like 'false' was kept as a string. The boolean worked before but didn't type-check and the docs say:

You probably only want to define a default value if you're expecting a String or Number value type.

So changed it to not have a default and modified the conditional