fix mkdocs issue

- introduced docker mkdocs build
- changed pages to nav in mkdocs.yml due to newer mkdocs version

.travis.yml

@@ -2,15 +2,17 @@ branches:
   only:
   - master
 language: groovy
-sudo: false
-install:
-- pip install --user mkdocs==0.17.5 mkdocs-material==2.9.4
+sudo: required
+services:
+ - docker
+before_install:
+- docker pull squidfunk/mkdocs-material
 script:
 - mvn clean test --batch-mode
 - |
   if [[ "${TRAVIS_PULL_REQUEST}" != "false" ]]
   then
-    cd documentation && mkdocs build --clean --verbose --strict && cd ..
+    cd documentation && docker run --rm -it -v ${PWD}:/docs squidfunk/mkdocs-material build --clean --verbose --strict && cd ..
   else
     # Only in case we are in master branch of the leading SAP repo we would like to deploy,
     # not from the forks.
@@ -25,7 +27,6 @@ script:
 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:

documentation/mkdocs.yml

@@ -1,5 +1,5 @@
 site_name: Jenkins 2.0 Pipelines
-pages:
+nav:
     - Home: index.md
     - Configuration: configuration.md
     - 'Library steps':