Fix broken links on `Capybara::Minitest::Assertions` API doc
Fix broken links on `Capybara::Minitest::Assertions` API doc

This change is extracted from #2190.

jnicklas/capybara,jnicklas/capybara,teamcapybara/capybara,jnicklas/capybara,teamcapybara/capybara,teamcapybara/capybara