Update nestjs.mdx (#472)

`@default(auth().id)` does not seem to be supported by prisma also made author and authorId optonal to align with the zModel code further down

Author: lsmith77

docs/quick-start/nestjs.mdx

@@ -69,8 +69,8 @@ model Post {
  updatedAt DateTime @updatedAt()
  title String
  published Boolean @default(false)
- author User @relation(fields: [authorId], references: [id])
- authorId Int @default(auth().id)
+ author User? @relation(fields: [authorId], references: [id])
+ authorId Int?
 }
 ```