CLN: Use of Iterable from collections.abc instead of typing.Iterable
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

looks fine, @WillAyd, @simonjayhawkins did we need something else besides this? I _think_ the intention here was to use typing.collection https://docs.python.org/3/library/typing.html#typing.Collection which was added in 3.6 as opposed to using Iterable from collections. Thanks @MomIsBestFriend 