Modified version constraint for pdepend/pdepend

Switched to the tilde comparison operator to make sure composer will not
grab the 2.x (or higher even) incompatible release from pdepend/pdepend.
Merge branch '1.5.x' of https://github.com/alcohol/phpmd into alcohol-1.5.x

Conflicts:
	composer.lock
Dependencies fixed.
Version number bumped for new 1.5.x release