Bump capybara from 2.15.3 to 2.15.4
Bump capybara from 2.15.3 to 2.15.4

Bumps [capybara](https://github.com/teamcapybara/capybara) from 2.15.3 to 2.15.4.
- [Changelog](https://github.com/teamcapybara/capybara/blob/master/History.md)
- [Commits](https://github.com/teamcapybara/capybara/compare/2.15.3...2.15.4)
rdunlop/unicycling-rulebook,rdunlop/unicycling-rulebook,rdunlop/unicycling-rulebook,rdunlop/unicycling-rulebook