Use yarn for CI steps

Author: adamwathan

.github/workflows/nodejs.yml

@@ -23,8 +23,8 @@ jobs:
         uses: actions/setup-node@v1
         with:
           node-version: ${{ matrix.node-version }}
-      - run: npm install
-      - run: npm run prepare
-      - run: npm test
+      - run: yarn
+      - run: yarn run prepare
+      - run: yarn test
         env:
           CI: true