Symfony-docs: Fix the current docs of SonataAdminBundle

[javiereguiluz]

Moved from https://github.com/symfony/symfony-marketing/issues/385

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Maybe you could help us changing this to the right docs:
http://symfony.com/doc/current/bundles/SonataAdminBundle/index.html

This leads to 2.x instead of 3.x, which is the current version of sonata

[OskarStark]

2.x is not supported anymore (same for the other sonata bundles)
3.x is current
and
master is...master and will be the next major

[javiereguiluz]

Thanks ... I've made those changes (and aliased "master" to "4.x"). It will be fixed once merged and deployed.

[Moltchalivyi-Koder]

https://symfony.com/doc/master/bundles/SonataAdminBundle/getting_started/the_form_view.html#configuring-the-form-mapper

No longer possible to do that :
$formMapper->add('title', 'text');
Instead:
$formMapper->add('title', TextType::class);
don't forget to add this line above the class :
use Symfony\Component\Form\Extension\Core\Type\TextType;

According to the official Sonata's doc:
https://sonata-project.org/bundles/admin/3-x/doc/getting_started/the_form_view.html#configuring-the-form-mapper