Diff-cover

* Fixes issue where report name would not respoect diff notation
https://github.com/Bachmann1234/diff_cover/issues/288 Thanks prescod for the
report.
* Drops Python 3.6 (This is why I bumped the major)

* Updates lockfile and tests to work with new pygment. Resolves [281](https://github.com/Bachmann1234/diff_cover/issues/281)

PR by me however, this was first identified and worked on by AdamWill in
[PR-280](https://github.com/Bachmann1234/diff_cover/pull/280). I absentmindly
stomped over that PR when I saw [Issue
281](https://github.com/Bachmann1234/diff_cover/issues/281) come in.

* Fixes issues when pylint identifies a multi line issue. Issue
[276](https://github.com/Bachmann1234/diff_cover/issues/276) Thanks kozlovsky

* Updates deps to allow newer Tomli versions Thanks kasium (PR by me cuse I
had to debug it some. He pointed out the original issue.)
* Fix to the tests to support a new version of pygments
* Fixed a test that was not asserting properly (thanks kalekundert
https://github.com/Bachmann1234/diff_cover/pull/264)

* Fixes issue where fail over was not being properly set by default. Thanks
kasium https://github.com/Bachmann1234/diff_cover/pull/262

* Replaces jinja-pluralize with native jinja's i18n
[Issue 259](https://github.com/Bachmann1234/diff_cover/issues/259)
* Some dev dep updates