feat: update Mocha plugin and drop ESLint 6 support

[AdamVig]

Commits

• feat: update Mocha plugin and drop ESLint 6 support
  BREAKING CHANGE:
  eslint-plugin-mocha no longer supports ESLint versions lower than
  7.0.0, so this configuration now requires a peer dependency of ESLint
  ^7.2.0.

[emroussel]

Unfortunately, I don't think create react app supports eslint 7 😕

https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/package.json#L47

Not sure if this change was for fms-ui or another repo, but it does mean that we wouldn't be able to update fms-ui to use this config until they support the next version of eslint

[AdamVig]

@emroussel That's a great catch! Looks like ESLint 7 support is almost ready, so it wouldn't be long before we could update fms-ui to use the latest version of this configuration: facebook/create-react-app#8978

More broadly, I try to keep the dependencies of this package up to date because it's used by every repository. Currently, this package's peer dependency on ESLint would actually prevent consumers from updating to ESLint 7, which is lame.

I'm comfortable merging this and waiting to update fms-ui until CRA adds support for ESLint 7, since there are plenty of other repositories that could immediately benefit from this update.