Log Message:
devel/ruby-rspec-support: update to 3.9.3

Update ruby-rspec-support to 3.9.3.

### 3.9.3 / 2020-05-02
[Full Changelog](http://github.com/rspec/rspec-support/compare/v3.9.2...v3.9.3)

Bug Fixes:

* Mark ripper as unsupported on Truffle Ruby. (Brandon Fish, #395)
* Mark ripper as unsupported on JRuby 9.2.0.0. (Brian Hawley, #400)
* Capture `Mutex.new` for our `RSpec::Support:Mutex` in order to
  allow stubbing `Mutex.new`. (Jon Rowe, #411)