minor #14124 [Notifier] Fix wrong package name for the RocketChat service (tambait)

This PR was squashed before being merged into the 5.1 branch.

Discussion
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[Notifier] Fix wrong package name for the RocketChat service

Package name "symfony/rocketchat-notifier" should be "symfony/rocket-chat-notifier"

Installation of the package using current package name returns InvalidArgumentException

```
[InvalidArgumentException]
Could not find a matching version of package symfony/rocketchat-notifier.
Check the package spelling, your version constraint and that the package is available
in a stability which matches your minimum-stability (stable).
```

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Commits
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b7928e5 [Notifier] Fix wrong package name for the RocketChat service

Author: OskarStark

notifier.rst

@@ -134,7 +134,7 @@ Service     Package                          DSN
 Slack       ``symfony/slack-notifier``       ``slack://default/ID``
 Telegram    ``symfony/telegram-notifier``    ``telegram://TOKEN@default?channel=CHAT_ID``
 Mattermost  ``symfony/mattermost-notifier``  ``mattermost://TOKEN@ENDPOINT?channel=CHANNEL``
-RocketChat  ``symfony/rocketchat-notifier``  ``rocketchat://TOKEN@ENDPOINT?channel=CHANNEL``
+RocketChat  ``symfony/rocket-chat-notifier`` ``rocketchat://TOKEN@ENDPOINT?channel=CHANNEL``
 ==========  ===============================  ============================================
 
 .. versionadded:: 5.1