Outdated PHPMD version

[IvanChepurnyi]

PHPMD version that currently locked in composer.lock results in different results of PHP Mess Detector. 2.3 has a weird bug in the coupling between objects rule that was fixed in 2.6, but codeclimate still uses outdated version.

[ravage84]

Yes, please update to PHPMD 2.7.0, which came out at the end of July.