Fix some style

.gitlab-ci.yml

checkstyle.xml

pom.xml

src/main/java/be/cylab/java/wowa/training/Example.java

...in/java/be/cylab/java/wowa/training/SolutionDistance.java

src/main/java/be/cylab/java/wowa/training/Trainer.java

...n/java/be/cylab/java/wowa/training/TrainerParameters.java

src/main/java/be/cylab/java/wowa/training/Utils.java

src/test/java/be/cylab/java/wowa/training/ExampleTest.java