[docs] update reference to getClientAddress()

[aradalvand]

The adapter-node README file mentions RequestEvent.clientAddress, but that's now a function: RequestEvent.getClientAddress().

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🦋 Changeset detected

Latest commit: 3a52085

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@sveltejs/adapter-node	Patch

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[benmccann]

#6237 for reference

[benmccann]

I added a changeset so the docs will be fixed in the published package. I feel like we should probably separate docs from publishing, but I guess that's for another time