v1.6.2

Bump to v1.6.2.

The v1.6.1 tag was created without having bumped the version in
canonicaljson.py. This means that installing from source at the v1.6.1 tag will install
the package with the wrong version in its metadata. The 1.6.1 artefacts
uploaded to PyPI did have the correct version; pip installing
directly from the archive resulted in a consistent version number.

There are no other changes in v1.6.2.

Full Changelog: v1.6.1...v1.6.2