[Doc] Updated some article for Symfony 4
[Doc] Updated some article for Symfony 4

yceruto/EasyAdminBundle,OskarStark/EasyAdminBundle,javiereguiluz/EasyAdminBundle,javiereguiluz/EasyAdminBundle,OskarStark/EasyAdminBundle,OskarStark/EasyAdminBundle,yceruto/EasyAdminBundle,yceruto/EasyAdminBundle