Correct Checkstyle clause in docs

[hlyakhovich]

Hi Patrick,

Correct me if I'm wrong but it looks like checkstyle:check binds to Maven's verify phase by default (docs). Thus it seems worth it to adjust the docs since mvn test is not going to run Checkstyle.

If mvn test is indeed what you had in mind, guess you could change the common-parent POM to bind Checkstyle to another phase but this could have ramifications in other projects only you are aware of as the POM maintainer.

The purpose of this PR is just to attract attention to the wording in docs, feel free to discard it.