Upgrade RSpec to 4.0.0 from 4.0.0.beta4

What does this MR do?

Stable version is now released so we don't need to keep using the beta version.

The other gems upgraded here were the result of running bundle update rspec-rails. They're not really necessary but since they're very small changes, I just decided to include them.

Changes:

• https://github.com/rspec/rspec-rails/compare/v4.0.0.beta4...v4.0.0#diff-9b8fab691c00b9e5380b19ce882f3271
• https://github.com/rspec/rspec-expectations/compare/v3.9.0...v3.9.1#diff-9b8fab691c00b9e5380b19ce882f3271
• https://github.com/flavorjones/loofah/compare/v2.4.0...v2.5.0#diff-4ac32a78649ca5bdd8e0ba38b7006a1e
• https://github.com/tzinfo/tzinfo/compare/v1.2.6...v1.2.7#diff-8b1c3fd0d4a6765c16dfd18509182f9d

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team