Disable cache for ubuntu cuda image building

- nvidia-docker mounts the host's driver libraries into the container
- when building an image on top of that, those libraries will get saved as empty into the next layer
  (they are usually overloaded by nvidia-docker runtime so it doesn't get noticed)
- when the host's gpu driver is updated, however, the old driver files remain and the new ones
  are mounted into the container -> driver libraries from multiple versions hanging around
  potentially causing issues. Don't allow it.

.gitlab-ci.yml

@@ -7,7 +7,7 @@ build-ubuntu-18.04:
   before_script:
     - echo "${CI_REGISTRY_PASSWORD}" | docker login -u "${CI_REGISTRY_USER}" "${CI_REGISTRY}" --password-stdin
   script:
-    - docker build --pull -t "${CI_REGISTRY}/${CI_PROJECT_PATH,,}:ubuntu-18.04" ubuntu-18.04
+    - docker build --no-cache --pull -t "${CI_REGISTRY}/${CI_PROJECT_PATH,,}:ubuntu-18.04" ubuntu-18.04
     - docker push "${CI_REGISTRY}/${CI_PROJECT_PATH,,}:ubuntu-18.04"
   after_script:
     - docker logout "${CI_REGISTRY}"