Graphviz install with apt-get

.gitlab-ci.yml

@@ -79,6 +79,7 @@ unit-test-job:   # This job runs in the test stage.
 pages:
   stage: deploy
   script:
+  - apt update
   - apt-get install graphviz
   - pip install -U sphinx m2r2 furo graphviz pyUML pydot gprof2dot
   - pip install -e .