Fix sphinx path and add test

.gitlab-ci.yml

@@ -163,6 +163,12 @@ test/ubuntu-python3:cuda-9.0:
 test/ubuntu-python3:cuda-10.1:
   extends: .test_template
   needs: ["ubuntu-python3:cuda-10.1:build"]
+  script:
+    - git clone --depth=1 --recursive https://github.com/espressomd/espresso
+    - cd espresso
+    - maintainer/CI/build_cmake.sh
+    - cd build
+    - make sphinx
 test/ubuntu:arm64:
   extends:
     - .test_template

docker/ubuntu-python3/Dockerfile-cuda-10.1

@@ -54,5 +54,6 @@ RUN tlmgr init-usertree \
 
 # install Python3 packages locally
 RUN pip3 install --user --upgrade 'sphinx>=2.0,!=2.1.0' sphinxcontrib-bibtex 'MDAnalysis==0.16' 'pint>=0.9'
+ENV PATH="/home/espresso/.local/bin:${PATH}"
 
 WORKDIR /home/espresso