Fixed a quoting bug of special characters in S3.
Populate both next_token and nextToken. Fixes #1968.

This bug was introduced due to an issue with how boto handled the nextToken
field in responses, which meant that it was exposed with the incorrect
name. The fix caused existing code to break, so now both versions are made
available. New code should use next_token.
Added release notes for 2.22.1.
Bumped to v2.22.1!
Merge branch 'hotfix-2.22.1'