Adjust PHPUnit 5 check to be consistent with others

[kostajh]

This is consistent with how other versions are checked, and also reduces esoteric bugs when PHPUnit_TextUI_ResultPrinter exists, even though the PHPUnit version is newer.

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update [X] Bug fix [ ] New feature [ ] Other, please explain:

What changes did you make? (Give an overview)

Make check consistent with others.

Which issue (if any) does this pull request address?

Fixes #174

Is there anything you'd like reviewers to focus on?