fix(ci): add missing yarn command

Author: benjie

.github/workflows/deploy.yml

@@ -22,6 +22,7 @@ jobs:
           node-version: 12
       - run: git config credential.helper "store --file=.git/credentials"
       - run: 'echo "https://benjie:${GITHUB_TOKEN}@github.com" > .git/credentials'
+      - run: yarn
       - run: yarn clean
       - run: yarn format
       - run: yarn build