Fix typo
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

thanks @felixdivo  @felixdivo this was applied to the 0.25.x branch. If you want it to be fixed for all versions going forward you'll need to make a PR against master. grr didn't notice this was not master :-< The GitHub UI doesn't make it obvious :/ Only saw it in my email. Okay sure, I didn't get your branching model. I'll apply it to master as well, that's the more important one. :smile: 