minor #5690 Updated the release process image (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
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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
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74b19ff Updated the release process image

Author: xabbuh