Merge pull request #40 from o-liver/buildMkdocs

Building documentation with `mkdocs` and aborting Travis build on error.

.travis.yml

@@ -1,2 +1,11 @@
 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; fi;
+cache:
+  directories:
+  - $HOME/.m2
+  - $HOME/.cache/pip