activate checkstyle validation

[romani]

failure like:

[INFO] --- maven-checkstyle-plugin:3.1.2:check (validate) @ methods-distance ---
[INFO] Starting audit...
[ERROR] /home/rivanov/java/github/sevntu-checkstyle/methods-distance
  /methods-distance/src/test/java/com/github/sevntu/
  checkstyle/domain/BaseCheckTestSupport.java:1: 
 Missing a header - not enough lines in file. [header]
[ERROR] /home/rivanov/java/github/sevntu-checkstyle/methods-distance/
  methods-distance/src/test/java/com/github/sevntu/
  checkstyle/domain/ExpectedDependencies.java:1: 
  Missing a header - not enough lines in file. [header]

revert 2aada5e to reproduce