message: Fix cache key and restore keys in ci.yaml.
  Fix a typo in the key assigned to the yarn cache, also
  update the restore key to use the yarn cache of a previous
  build compatible with the os and node version.
diff: @@ -39,9 +39,10 @@ jobs:
  id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
  with:
  path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
  - key: ${{ runner.os }}-${{ matrix.node_version }}--yarn-${{ hashFiles('**/yarn.lock') }}
  + key: yarn-${{ runner.os }}-${{ matrix.node_version }}-${{ hashFiles('**/yarn.lock') }}
  restore-keys: |
  - ${{ runner.os }}-yarn-
  + yarn-${{ runner.os }}-${{ matrix.node_version }}-
  + yarn-${{ runner.os }}-
  - name: Use Node.js ${{ matrix.node_version }}
  uses: actions/setup-node@v1
  