v1.5.3

Bumping release due to inconsistency in python 3.6 support that affected pypi
jwcrypto-1.5.3.tar.gz.sha512sum.txt
jwcrypto-1.5.3.tar.gz

What's Changed

• Drop python 3.6 and 3.7 and add 3.11 support by @simo5 in #340

Full Changelog: v1.5.2...v1.5.3