[Checkins] [zopefoundation/zc.relation] 14b5b0: Fix linting issues

[Jürgen Gmach]

  Branch: refs/heads/master
  Home:   https://github.com/zopefoundation/zc.relation
  Commit: 14b5b04b87ca86b71b04e80f0b0ed2dd29223bf4
      https://github.com/zopefoundation/zc.relation/commit/14b5b04b87ca86b71b04e80f0b0ed2dd29223bf4
  Author: Jürgen Gmach <juergen.gmach at googlemail.com>
  Date:   2020-05-17 (Sun, 17 May 2020)

  Changed paths:
    M src/zc/relation/catalog.py
    M tox.ini

  Log Message:
  -----------
  Fix linting issues

... which arise with the new flake8 version.

`tests` is no longer a valid flake8 param, as it is no top level
directory.

As it is a subfolder of the `src` folder, it gets linted anyway.

Also, do not use `l` as a variable name.

modified:   tox.ini
modified:   src/zc/relation/catalog.py