Since urllib3 v2 the re-export of connection.HTTPConnection in
urllib3.connectionpool was removed.
In this commit we use urllib3.connection where needed. Some references
to connectionpool.HTTPConnection are still there for backward
compatibility.
Closes#688
Format with line length 110 to match flake8
make black part of linting check
Update travis spec for updated black requirements
Add diff output for black on failure
update changelog
This refactoring includes some PEP-8 compliance changes, as well as some more
complete testing to ensure that we're in fact serving everything out of
cassettes when we thing we are.
Incidentally, it also includes fixes for #3 and #4
