ci: test with updated package versions

[juarezr]

This PR has the objective of keeping petl testing with updated packages

Changes

1. Removed upper limit on dependencies
2. Fix CVE-2021-33430
3. Announce python 3.9 in package

Checklist

Use this checklist for assuring the quality of pull requests that include new code and or make changes to existing code.

• [ ] Source Code rules apply:
  • [ ] Includes unit tests
  • [ ] New functions have docstrings with examples that can be run with doctest
  • [ ] New functions are included in API docs
  • [ ] Docstrings include notes for any changes to API or behaviour
  • [ ] All changes are documented in docs/changes.rst
• [X] Versioning and history tracking rules apply:
  • [X] Using atomic commits when possible
  • [X] Commits are reversible when possible
  • [X] There is no incomplete changes in the pull request
  • [ ] There is no accidental garbage added in source code
• [X] Testing rules apply:
  • [X] Tested locally using tox / pytest
  • [ ] Automated testing passes (see CI)
  • [ ] Unit test coverage has not decreased (see Coveralls)
• [ ] State of these changes is:
  • [ ] Just a proof of concept
  • [ ] Work in progress / Further changes needed
  • [X] Ready to review
  • [X] Ready to merge

[coveralls]

Coverage remained the same at 91.759% when pulling e4d81f043d75900b4323b996e35ca6e0bb122fb4 on juarezr:min-package-versions into 1ed38a6c2a97619f02d234a1194c7f3eba69a1ec on petl-developers:master.