minor #5690 Updated the release process image (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
----------

Updated the release process image

In #5471 we tried to update the image of this page: http://symfony.com/doc/current/contributing/community/releases.html

It's clear that I made some mistake with the image path, because the old image is still displayed. This is a second attempt at updating that image.

Commits
-------

74b19ff Updated the release process image