Upgrade dependencies for CVE-2020-7660

[captain-kark]

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When using this project as a template, I was given security warnings concerning https://github.com/advisories/GHSA-hxcc-f52p-wc94

What I did to fix this after generating a new project from this template:

mochajs/mocha#4375

• update https://github.com/cloudflare/worker-typescript-template/blob/9a1574a532bcdd3da55e5b19e5d9fb57df4078c2/package.json#L21

    "mocha": "^8.1.0",

webpack/webpack#11309

• https://github.com/webpack/webpack/issues/11309#issuecomment-674128535

Afterwards, the example npm test and npm run build succeeded.