Configure pep8speaks to use 88 character line length

[mkelley]

I'm happy with black formatting, which uses an 88 character line length limit. Astropy has also moved to formatting code with black. Shall we change pep8speaks to use an 88 character limit? (see #394 for an example with 80 character line length but code formatted with black).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.52%. Comparing base (1315915) to head (f59f7a7). Report is 22 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #395 +/- ## ======================================= Coverage 77.52% 77.52% ======================================= Files 81 81 Lines 7096 7096 ======================================= Hits 5501 5501 Misses 1595 1595 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.