Bump tox-travis from 0.12 to 0.13 (#326)

Bumps [tox-travis](https://github.com/tox-dev/tox-travis) from 0.12 to 0.13.
- [Release notes](https://github.com/tox-dev/tox-travis/releases)
- [Changelog](https://github.com/tox-dev/tox-travis/blob/master/HISTORY.rst)
- [Commits](tox-dev/tox-travis@0.12...0.13)

---
updated-dependencies:
- dependency-name: tox-travis
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/requirements_dev.txt

@@ -1,7 +1,7 @@
 -r requirements.txt
 pytest-cov==4.0.0
 tox==3.27.0
-tox-travis==0.12
+tox-travis==0.13
 codecov==2.1.12
 coverage==6.5.0
 flake8==6.0.0