1.21.0

✨ New Features

• Allow a Proc to be used as an interaction_handler (#436) @DamienRobert

📚 Documentation

• Removed dead links from README (#477) @ssimontis

🏠 Housekeeping

• Unpin mocha version and fix deprecation warnings for mocha v1.11.1 (#480) @floehopper
• Pin mocha at 1.9.x to fix CI failures (#478) @mattbrictson
• Add changelog_uri to metadata to easily link from rubygems.org (#473) @nickhammond
• Automatically maintain release notes using GitHub Actions (#472) @mattbrictson