Request: don't mutate positional-only signature marker

[willfrey]

Hi there!

Thanks for all your work on mutmut!

As if Python 3.8, you can use the / character in a function/method signature definition to mark all the preceding parameters are being positional-only. The details are in PEP 570.

Currently, mutmut will find the / character in the signature and mutate it to be a *. mutmut doesn't mutate the keyword-only marker *, so it'd be nice if mutmut also left the / alone.

Thanks!

[castarco]

True, I just found that it generates a lot of false positives.

[boxed]

You want to give this a shot?