CLN: fix mypy warnings/errors
When I run `mypy pandas` locally I get a handful of complaints.  This fixes about half of them.  The other half are about `FixedOffset` which IIRC we are handling elsewhere.

cc @simonjayhawkins 
What version of mypy are you using and what are the errors exactly? I'm very hesitant to add `# type: ignore` anywhere, especially if there's no urgency to do so

@angelaambroz fixed the issue with FixedOffset upstream in TypeShed and I think that will make its way into mypy 0.75 0.740 Hello @jbrockmendel! 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 2019-11-02 02:37:11 UTC thanks @jbrockmendel 