Log Message:
devel/ruby-rspec-core: update to 3.8.0

### 3.8.0 / 2018-08-04
[Full Changelog](http://github.com/rspec/rspec-core/compare/v3.7.1...v3.8.0)

Enhancements:

* Improve shell escaping used by `RSpec::Core::RakeTask` and `--bisect` so
  that it works on `Pathname` objects. (Andrew Vit, #2479)
* Nicely format errors encountered while loading files specified
  by `--require` option.  (Myron Marston, #2504)
* Significantly improve the performance of `--bisect` on platforms that
  support forking by replacing the shell-based runner with one that uses
  forking so that RSpec and the application environment can be booted only
  once, instead of once per spec run. (Myron Marston, #2511)
* Provide a configuration API to pick which bisect runner is used for
  `--bisect`. Pick a runner via `config.bisect_runner = :shell` or
  `config.bisect_runner = :fork` in a file loaded by a `--require`
  option passed at the command line or set in `.rspec`. (Myron Marston, #2511)
* Support the [XDG Base Directory
  Specification](https://specifications.freedesktop.org/basedir-spec/latest/)
  for the global options file. `~/.rspec` is still supported when no
  options file is found in `$XDG_CONFIG_HOME/rspec/options` (Magnus Bergmark, #2538)
* Extract `RSpec.world.prepare_example_filtering` that sets up the
  example filtering for custom RSpec runners. (Oleg Pudeyev, #2552)

Bug Fixes:

* Prevent an `ArgumentError` when truncating backtraces with two identical
  backtraces. (Systho, #2515, Benoit Tigeot, #2539)