Update Dockerfile

Dockerfile

 # For finding latest versions of the base image see
 # https://github.com/SwissDataScienceCenter/renkulab-docker
-ARG RENKU_BASE_IMAGE=renku/renkulab-py:3.8-7bd410d
+ARG RENKU_BASE_IMAGE=renku/renkulab-py:3.7-0.7.3
 FROM ${RENKU_BASE_IMAGE}
 
 # add Visual Studio Code editor