[cloudflare] Service Worker

參考 

https://blog.cloudflare.com/cloudflare-workers-unleashed/

https://github.com/cloudflare/worker-examples

https://github.com/cloudflare/worker-examples/tree/master/examples/edge-cache-html

https://levelup.gitconnected.com/use-cloudflare-javascript-workers-to-deploy-you-static-generated-site-ssg-1c518e078646