ENH: Make Series.update() use objects coercible to Series
- [x] closes #33215 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Allows `Series.update()` to accept objects that can be coerced into a `Series`, like a `dict`. This mirrors the existing behavior of `DataFrame.update()`.
Hello @dericke! 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 2020-04-26 01:39:36 UTC thanks @dericke 