add graphviz im docker image

Dockerfile

@@ -2,6 +2,11 @@
 ARG BASE_IMAGE=registry.git.rwth-aachen.de/jupyter/profiles/rwth-courses:latest
 FROM ${BASE_IMAGE}
 
+# Install graphviz
+USER root
+RUN apt-get update && apt-get install -y graphviz git
+USER jovyan
+
 # Install packages via requirements.txt
 ADD requirements.txt .
 RUN pip install -r requirements.txt