Fix PR template from fix_lint to fix
Please, make sure you address all the checklists (for details on how see
[development documentation](http://tox.readthedocs.org/en/latest/development.html#development))!
-- [ ] ran the linter to address style issues (`tox -e fix_lint`)
+- [ ] ran the linter to address style issues (`tox -e fix`)
- [ ] wrote descriptive pull request text
- [ ] ensured there are test(s) validating the fix
- [ ] added news fragment in `docs/changelog` folder
