v2.4.0

Notable changes

• 👷 Optimize CI build
• 💥 Drop IIFE in favor of UMD bundle
• ✅ Improve test structure
• 🔧 Update Rollup config file to build UMD bundle
• ➕ Use @reallyland/tsconfig and @reallyland/tslint-config
• ✨ Use shx for cross-platform commands support, e.g. rm -rf
• 📝 Update doc to include Contributing section and new demo button