Update ruby-simplecov to 0.19.0.


0.19.0 (2020-08-16)
==========

## Breaking Changes
* Dropped support for Ruby 2.4, it reached EOL

## Enhancements

* observe forked processes (enable with SimpleCov.enable_for_subprocesses).
  See [#881](simplecov-ruby/simplecov#881), thanks
  to [@robotdana](https://github.com/robotdana)

* SimpleCov distinguishes better that it stopped processing because of a
  previous error vs. SimpleCov is the originator of said error due to
  coverage requirements.

## Bugfixes

* Changing the `SimpleCov.root` combined with the root filtering didn't
  work.  Now they do! Thanks to
  [@deivid-rodriguez](https://github.com/deivid-rodriguez) and see
  [#894](simplecov-ruby/simplecov#894)

* in parallel test execution it could happen that the last coverage result
  was written to disk when it didn't complete yet, changed to only write it
  once it's the final result

* if you run parallel tests only the final process will report violations of
  the configured test coverage, not all previous processes

* changed the parallel_tests merging mechanisms to do the waiting always in
  the last process, should reduce race conditions

## Noteworthy

* The repo has moved to https://github.com/simplecov-ruby/simplecov -
  everything stays the same, redirects should work but you might wanna
  update anyhow

* The primary development branch is now `main`, not `master` anymore.  If
  you get simplecov directly from github change your reference.  For a while
  `master` will still be occasionally updated but that's no long term
  solion.