Bump sha.js and web-ext (#71)

Removes [sha.js](https://github.com/crypto-browserify/sha.js). It's no longer used after updating ancestor dependency [web-ext](https://github.com/mozilla/web-ext). These dependencies need to be updated together.


Removes `sha.js`

Updates `web-ext` from 8.2.0 to 8.9.0
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@8.2.0...8.9.0)

---
updated-dependencies:
- dependency-name: sha.js
  dependency-version: 
  dependency-type: indirect
- dependency-name: web-ext
  dependency-version: 8.9.0
  dependency-type: direct:development
...

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