Fix output step name in docker image build

      - uses: actions/checkout@v2

      # https://stackoverflow.com/questions/59810838/how-to-get-the-short-sha-for-the-github-workflow

      - name: Set outputs

        id: vars

        id: commit

        run: echo "::set-output name=sha_short::$(git rev-parse --short HEAD)"

      - name: Set branch name

        id: branch