Update composer.lock

[Federkun]

After the first composer install I get a

[Doctrine\DBAL\DBALException]
Unknown database type json requested, Doctrine\DBAL\Platforms\MySQL57Platform may not support it.

when I try to create the db's schema. It's a feature available since 2.6 version of dbal, but right now it's locked to v2.5.10.

So, fork => composer install => composer update => push

[jewome62]

@dunglas with #23 we use postgresql

[dunglas]

Done in #24, thanks.