Prisma

I am confused with how a subscription endpoint is exposed via `graphql-yoga`

I have the following options config:

```
 const options = {
    port: PORT,
    cors: {
      credentials: true,
      origin:
        process.env.NODE_ENV === 'production' &amp;&amp; !process.env.FORCE_DEV
          ? ['<https://xxx.app>', /xxx-(\w|-)+\.now\.sh/g, /xxx\.app/]
          : [/localhost/]
    },
    endpoint: '/graphql',
    subscriptions: '/subscriptions',
    playground: '/playground'
  }
```

my question is, what is the websocket `uri` that i'd pass into `apollo-client`