Merge pull request #37 from mercari/micnncim/docker-workflow

Use secret for docker username in workflow

.github/workflows/docker.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Login to DockerHub
         uses: docker/login-action@v1 
         with:
-          username: ${{ github.repository_owner }}
+          username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
 
       - name: Output version