Re-enable eslint-plugin-promise as it now supports ESLint 8

[qyurila]

Currently the config file has eslint-plugin-promise plugin and rules commented-out. The comment says it's disabled as the plugin doesn't support ESLint 8 yet.

Since eslint-plugin-promise 6.0.0 introduced ESLint 8 support, I think it can be re-enabled now.

[fregante]

Note that this plugin is now part of the eslint-community group so it might get more attention and support as a consequence, which is why it was probably fixed now.