symfony/yaml components is locked to be 3.x

Explicitly specified symfony/yaml to be of version 3.x

If not specified then Composer will install latest version
(which at the time of writing happens to be 4.x) and Yaml
component from 4.x is not compatible with 3.x (which is at
the moment is used by Modera Foundation)

Now it should be possible to use Symfony 3 as well

v0.2

[MPFE-1051] ran 'composer update', latest components fetched, now it …

Symfony 2 tested version

v0.1

[MPFE-1051] styleci integration removed