CLN: f-string formatting
Ref to [#29547](https://github.com/pandas-dev/pandas/issues/29547)

- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Replacing strings interpolated with .format() with strings interpolated with f-strings
Hello @monicaw218! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





















There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-02-11 04:36:39 UTC Great thanks @monicaw218