"images/request-flow.png" references Symfony2

images/request-flow.png has "Symfony2 Kernel" instead of "Symfony3 Kernel".

I'd submit a PR, but I'm not sure how the graphic is generated.

[javiereguiluz]

Updating these images is very time-consuming ... so we usually don't do it 😢 However, if we update this, we should replace Symfony2 by Symfony to make it future-proof. Thanks!

If that's the case, I'm happy to fill in the "2" with the background color and submit a PR.

Is that okay with you?

[javiereguiluz]

@danielcotton that would be a dirty hack ... so I love it 😁