cortexutils not installed in RT4 Responder Docker Image

Running the Mailer responder in Docker throws a ModuleNotFound error.: 

Traceback (most recent call last):
  File "/worker/RT4/rt4.py", line 4, in <module>
    from cortexutils.responder import Responder
ModuleNotFoundError: No module named 'cortexutils'

Is it possible to correct this Docker image present in the Docker Hub repository ?

responders/RT4/requirements.txt

@@ -1,4 +1,5 @@
 defang
 jinja2
 rt
-requests
+requests
+cortexutils