fix express.js example

[Livshitz]

Should be using createServerAdapter adapter to convert to express-compatible handler. Based on this issue conversation: #246 (comment)

Description

v5 changes created regression in the way express handled router.handle. The right way is anyway to use createServerAdapter (from @whatwg-node/server) to make itty's router express-compatible.

Related Issue

Link to the related issue: #246 (comment)

Type of Change (select one and follow subtasks)

• [] Documentation (README.md)
• Maintenance or repo-level work (e.g. linting, build, tests, refactoring, etc.)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
  • I have included test coverage
• Breaking change (fix or feature that would cause existing functionality/userland code to not work as expected)
  • Explain why a breaking change is necessary:
• This change requires (or is) a documentation update
  • I have added necessary local documentation (if appropriate)
  • I have added necessary itty.dev documentation (if appropriate)

[kwhitley]

Thanks, Elya! <3