vercel integration: fix the GitHub link for durable streams

The @electric-sql/durable-streams npm package is non-existent but I take
it this is a draft doc referencing not-yet-existing stuff, so I haven't
touched those.

Author: alco

website/docs/integrations/vercel.md

@@ -64,7 +64,7 @@ const result = await streamText({
 
 - [Durable Streams documentation](/products/durable-streams)
 - [Vercel AI SDK documentation](https://sdk.vercel.ai)
-- [Durable Streams GitHub](https://github.com/electric-sql/durable-streams)
+- [Durable Streams GitHub](https://github.com/durable-streams/durable-streams)
 
 ## Deploying Electric on Vercel