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
• Versioning and history tracking rules apply:
  • Using atomic commits when possible
  • Commits are reversible when possible
  • There is no incomplete changes in the pull request
  • There is no accidental garbage added in source code
• Testing rules apply:
  • 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
  • Ready to review
  • Ready to merge

[coveralls]

Coverage remained the same at 91.759% when pulling e4d81f0 on juarezr:min-package-versions into 1ed38a6 on petl-developers:master.