Update rules-of-workflows.mdx

Author: elithrar

src/content/docs/workflows/build/rules-of-workflows.mdx

@@ -306,7 +306,7 @@ export default {
     let instanceId = getTransactionId() // e.g. assuming transaction IDs are unique
     // or: compose a composite ID and store it in your database
     // so that you can track all instances associated with a specific user or merchant.
-    let instanceId = `${getUserId(request}-${await crypto.randomUUID().slice(0, 6)}`
+    instanceId = `${getUserId(request}-${await crypto.randomUUID().slice(0, 6)}`
     let { result } = await addNewInstance(userId, instanceId)
     let instance = await env.MY_WORKFLOW.create({
     	id: userId,