Update composer.lock for PHPUnit 6.5 and Codeception 2.3.8
Update composer.lock for PHPUnit 6.5 and Codeception 2.3.8

Codeception had to be updated to 2.3.8 because it is the first version
compatible with PHPUnit 6.5.

Signed-off-by: Daniel Calviño Sánchez <bd7629e975cc0e00ea7cda4ab6a120f2ee42ac1b@gmail.com>

desaintmartin/gallery,desaintmartin/gallery,desaintmartin/gallery