Description of the desired feature

Our code of conduct is based on the Contributor Covenant v2.0 (#673), and the latest version is v2.1. The difference between v2.0 and v2.1 is small (https://github.com/EthicalSource/contributor_covenant/blob/release/changelog), so updating from v2.0 to v2.1 should be an easy job.

We should also add PyGMT (and GMT) to the long list of adopters (https://www.contributor-covenant.org/adopters/) by submitting a pull request (https://github.com/EthicalSource/contributor_covenant/blob/release/README.md#registering-your-community-as-an-adopter).