We initially ignored the `composer.lock` because it generated a lock of rebase on PR when someone updated it and the master updated it too.
Now we have less contributions (sadly) so I think we won't run against that problem.
Also, it'll solve issue about people cloning the master and got angry because composer eat all the available memory to determine packages to install.
It'll also be much easier to make release.
Scrutinizer & Travis will be faster too.