Fix file permissions

[Djennez]

chown in start.sh was changed from /var/www/ to /var/www/.wp-cli to speed up the starting process. But this has impications for Linux systems which can get into file permission issues this way.

[bintzandt]

Temporary fix seems to be to add docker exec -ti basic-wordpress /bin/bash -c 'chown -R www-data: /var/www/html after echo "Installing WordPress for $CONTAINER..." in start.sh.