anchor.diff: -FROM python:3.7
  +FROM stencila/executa:20200414.1
  +
  +# This is necessary because the executa image
  +# defaults to a guest user.
  +USER root
   
   # Create `worker` user and use it's home dir
   RUN useradd -m worker
  
positive.code: 
  # Run Celery as the user `worker`
  USER worker
  CMD celery worker --app worker --queues stencila --hostname worker@stencila
  
negative.code: 
  # Install Python requirements
  COPY requirements.txt ./  
  RUN pip3 install --no-cache-dir -r requirements.txt
  
  # Copy Python app files
  COPY . ./
  