minor symfony#1928 docs: fix mercure config-file (Chris53897)

This PR was merged into the 2.x branch.

Discussion
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docs: fix mercure config-file

changed since mercure 0.16.2

Please see
https://mercure.rocks/docs/UPGRADE

Commits
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eebfa3b docs: fix mercure config-file

src/Turbo/CONTRIBUTING.md

@@ -7,7 +7,7 @@ Start a Mercure Hub:
         -e MERCURE_PUBLISHER_JWT_KEY='!ChangeMe!' \
         -e MERCURE_SUBSCRIBER_JWT_KEY='!ChangeMe!' \
         -p 3000:3000 \
-        dunglas/mercure caddy run -config /etc/caddy/Caddyfile.dev
+        dunglas/mercure caddy run -config /etc/caddy/dev.Caddyfile
 
 Install the test app: