DOC fix misspelling of countries
simple misspelling fix. From "counties" to "countries"
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

Thanks for the PR, but this is correct (there is a "Dade" county in Florida for example). Please feel free to take any other issue labeled `good first issue`