fix pip command

Dockerfile

@@ -4,7 +4,7 @@ FROM ${BASE_IMAGE}
 
 # Install packages via requirements.txt
 ADD requirements.txt .
-RUN pip3 install -r requirements.txt
+RUN pip install -r requirements.txt
 
 # .. Or update conda base environment to match specifications in environment.yml
 ADD environment.yml /tmp/environment.yml