Updated services configuration exemple

[mickaelandrieu]

Symfony 3.3 introduced an easier way to declare service => http://symfony.com/blog/new-in-symfony-3-3-optional-class-for-named-services

[fabpot]

What about removing all classes then? Why just one of them?

[GuilhemN]

@fabpot i think that's for those using sf < 3.3

[dunglas]

I agree with @fabpot, we should remove all class in existing examples and add a new one with class set for people using Symfony < 3.3.

[mickaelandrieu]

All comments adressed, thank you :)

[GuilhemN]

:+1:

[dunglas]

Thanks @mickaelandrieu