remove docu generation

since pip install fails caused by outdated python version

.travis.yml

@@ -1,14 +1,10 @@
 language: groovy
 sudo: false
-install:
-- pip install --user mkdocs mkdocs-material
 script:
 - mvn test -B
-- if [[ "${TRAVIS_PULL_REQUEST}" != "false" ]]; then cd documentation && mkdocs build --clean --verbose --strict && cd ..; fi;
 cache:
   directories:
   - $HOME/.m2
-  - $HOME/.cache/pip
 after_success:
   - mvn -DrepoToken=$COVERALLS_REPO_TOKEN org.jacoco:jacoco-maven-plugin:report org.eluder.coveralls:coveralls-maven-plugin:report
 notifications: