On v4, we used the default nodejs resolution logic to allow ES modules in dependencies.
This created a breaking change of forcing users of this action
to use the .cjs extension instead of .js in config files.
With this fix, we now bundle the action with rollup to allow ES modules
in dependencies, while keeping the support for .js config files.
With this change, the default config file was returned back to .js instead of
.cjs.
Fixes#194
BREAKING CHANGE: this includes breaking changes from commitlint v9,
like the fact that `improvement` type is now rejected in `@commitlint/config-conventional`.