title: ImportError: cannot import name 'firestore'
body: <p>I'm doing a dataflow streaming app that would write in firestore, when I run on DirectRunner it works, but when I run on DataflowRunner it doesn't works. what is the error? my <code>requirements.txt</code> is:</p>
  
  <pre><code>apache-beam[gcp,test]==2.19.0
  google-cloud-pubsub
  google-cloud-firestore==0.29.0
  </code></pre>
  
  <p>the row of code that throws the exeption is:</p>
  
  <pre><code>from google.cloud import firestore
  db = firestore.Client(project=project)
  </code></pre>