Updated code of conduct to contributor covenant v2.1

[santacodes]

Description

Fixes #4160

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.58%. Comparing base (0421fc3) to head (04b5fa1).
Report is 206 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4171   +/-   ##
========================================
  Coverage    99.58%   99.58%           
========================================
  Files          288      288           
  Lines        21770    21770           
========================================
  Hits         21679    21679           
  Misses          91       91           

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[kratman]

@santacodes This same issue is on pybamm-cookiecutter. Can you fix it there as well?

[santacodes]

@santacodes This same issue is on pybamm-cookiecutter. Can you fix it there as well?

Thank you for noticing, yes I did fix it!

[agriyakhetarpal]

We should adapt Lychee to the cookiecutter repository as well, @santacodes.