Remove capybara from dev deps

[mbie]

Dependabot tries to update capybara #108 but the previous attempts were closed (#30, #32, #33, #34, #35). Today, it seems that the capybara gem is not used anymore in the repository so it's better to remove it just to not bother with the updates in the future.

Review

• Document code according to Getting Started with Yard.
• All tests are passing.
• Test manually.
• Get approval.

Pre-merge checklist

• The PR relates to a single subject with a clear title and description in grammatically correct, complete sentences.
• Verify that feature branch is up-to-date with master (if not - rebase it).
• Double check the quality of commit messages.
• Squash related commits together.