[AIRFLOW-4433] - Add missing type in DockerOperator doc string (#5205)
[AIRFLOW-4433] - Add missing type in DockerOperator doc string (#5205)

Add missing type in DockerOperator docstring for the volumes params

(cherry picked from commit 7e2a8072abc9f7af96f27218d7ab5bdd8e551e58)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow