Fixes regression on Windows introduced in 3.x branch

Fixed

• Make __dirname declaration cross-platform (was previously failing on Windows). See nodejs/node#37845
• Introduce small delay in request fail check test while certificate is being provisioned to ensure tests pass with Let’s Encrypt staging server.

ESM

Changed

• Breaking change: Is now an ECMAScript Modules (ESM) project.
• Now includes the latest Let’s Encrypt certificate authority root certificate for the staging environment. (This is automatically injected into your Node.js environment when running the server in staging mode and is used during testing.)
• Dev: now using @small-tech/esm-tape-runner.
• Dev: replaced tap-spec and tap-nyc with @small-tech/tap-monkey.

Fixed

• No longer crashes when checking for certificate renewal. (#34)
• Tests now run properly in staging mode.

Improved

• npm package size is now 193.1kb (down from 345kb previously).