update composer 

Stephy renamed his package and added releases. 

I'm not sure which version constraint is the best ('2.0.*' ~2.0). 
So if you want me to change it to something else please let me know.
removed lib dependency updated constraint
Merge pull request #21 from Miliooo/patch-1

update composer
Add dutch translations
Merge pull request #22 from Miliooo/patch-2

Add dutch translations
Merge remote-tracking branch 'sonata-project/master'