Can't run sample project that uses ISR on Cloudflare via @vinext/cloudflare 1.0.0-beta.6

Steps to reproduce:
1. Clone project https://github.com/grabmateusz/isr-on-demand-revalidate-issue
2. Migrate it to vinext as per vinext README.md
OR
Take code that already went through that route:
https://github.com/grabmateusz/isr-on-demand-revalidate-issue/pull/3
3. Try to deploy this code to Cloudflare Workers
4. Visit /isr

Expected:
ISR version of the route is rendered without a problem

Current:
500 response code, no root cause in logs

Clone the linked sample project, review the migration described in README.md and pull request #3, then deploy it to Cloudflare Workers and visit /isr. Compare the expected ISR response with the current 500 response and inspect the available logs. Done means the ISR route renders successfully on the worker without the unexplained failure.

Written by the indexing model from the issue text.