add platform emulator

.github/workflows/docker.yml

@@ -12,6 +12,8 @@ jobs:
     steps:
       - name: checkout code
         uses: actions/checkout@v2
+      - name: setup platform emulator
+        uses: docker/setup-qemu-action@v1
       - name: setup multi-arch docker build
         uses: docker/setup-buildx-action@v1
       - name: Login to DockerHub