Log Message:
devel/ruby-concurrent-ruby: update to 1.1.6

Update ruby-concurrent-ruby to 1.1.6.

## Release v1.1.6, edge v0.6.0 (10 Feb 2020)

concurrent-ruby:

* (#841) Concurrent.disable_at_exit_handlers! is no longer needed and was deprecated.
* (#841) AbstractExecutorService#auto_terminate= was deprecated and has no effect.
  Set :auto_terminate option instead when executor is initialized.