minor #965 [Site] Fixing docker config for mercure (weaverryan)

This PR was merged into the 2.x branch.

Discussion
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[Site] Fixing docker config for mercure

| Q             | A
| ------------- | ---
| Bug fix?      | yes (to the site)
| New feature?  | no
| Tickets       | None
| License       | MIT

The flag was wrong, so mercure wouldn't start property. Helps with #963

Cheers!

Commits
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3f4712e [Site] Fixing docker config for mercure

Author: weaverryan

ux.symfony.com/docker-compose.yml

@@ -13,7 +13,7 @@ services:
       MERCURE_EXTRA_DIRECTIVES: |
         cors_origins https://127.0.0.1:9044
     # Comment the following line to disable the development mode
-    command: /usr/bin/caddy run -config /etc/caddy/Caddyfile.dev
+    command: /usr/bin/caddy run --config /etc/caddy/Caddyfile.dev
     volumes:
       - mercure_data:/data
       - mercure_config:/config