ci: upgrade setup-node to v2

Author: susisu

.github/workflows/ci.yml

@@ -15,12 +15,11 @@ jobs:
           - '14'
           - '16'
     steps:
-      - name: Checkout
-        uses: actions/checkout@v2
-      - name: Set up Node.js ${{ matrix.node-version }}
-        uses: actions/setup-node@v1
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node-version }}
+          cache: 'yarn'
       - run: yarn install --frozen-lockfile
       - run: yarn lint
       - run: yarn test