Since Moodle 3.4, we require php 7.0.0 (link).

In the other side, moodlehq/behat-extension declares php as (old) requirement (link).

This issue is about to:

• raise the requirement to php 7.0.0, for 34_STABLE and up.
• paralel, decide if, for 33_STABLE, the same should be applied for php 5.6.5.
• regenerate composer.lock, it should enable a number of updates.
• verify phpunit and behat continue working without problems.

(This issue was detected when working on MDL-62620 )