Update MIME-Base64 to CPAN version 3.16

Update MIME-Base64 to CPAN version 3.16

[DELTA]

3.16 2020-09-26
  - Convert the build to Dist::Zilla to ensure we're releasing well built packages
  - Ensure all tests are using strict and warnings (thanks, Nicolas R).
  - Cleanup this change log
  - Add a .mailmap to cleanup our contributors list
  - Use `our` instead of `use vars`
  - Bump the required Perl version to v5.6.2