Update ruby-rspec-rails to 4.0.1.
### 4.0.1 / 2020-05-16
Bug Fixes:
* Remove warning when calling `driven_by` in system specs. (Aubin Lorieux,
#2302)
* Fix comparison of times for `#at` in job matchers. (Jon Rowe, Markus
Doits, #2304)
* Allow `have_enqueued_mail` to match when a sub class of
`ActionMailer::DeliveryJob` is set using
`<Class>.delivery_job=`. (Atsushi Yoshida #2305)
* Restore Ruby 2.2.x compatibility. (Jon Rowe, #2332)
* Add `required_ruby_version` to gem spec. (Marc-André Lafortune, #2319,
#2338)