Swap eslint for prettier

Prettier is closer to rustfmt than eslint, and the eslint action we were
using was deprecated, so I've swapped it out.

This has the nice bonus of not needing errors to be manually fixed,
prettier will automatically do it for us.

Closes: #48

Author: lpil

.github/workflows/linter.yml

@@ -21,8 +21,8 @@ jobs:
       # Install your dependencies
       - run: npm ci
 
-      # Run ESLint
-      - uses: eslint/github-action@v0
+      # Check JavaScript code formatting
+      - run: npm run lint
 
       # Run Stylelint
       - uses: actions-hub/stylelint@v1.1.3