Log Message:
devel/ruby-zeitwerk: update to 2.4.0

Update ruby-zeitwerk to 2.4.0.

2.4.0 (15 July 2020)

* Zeitwerk::Loader#push_dir supports an optional namespace keyword argument.
  Pass a class or module object if you want the given root directory to be
  associated with it instead of Object.  Said class or module object cannot
  be reloadable.

* The default inflector is even more performant.