iot: fix broken link in readme
## Authentication
* Create a project with the [Google Cloud Console][cloud-console], and enable
- the [Cloud IoT Core API][].
+ the [Cloud IoT Core API][cloud-iot-api].
* From the Cloud Console, create a service account,
download its json credentials file, then set the `GCLOUD_PROJECT` and
`GOOGLE_APPLICATION_CREDENTIALS` environment variable:
```
[cloud-console]: https://console.cloud.google.com
-[vision-api]: https://console.cloud.google.com/apis/api/cloudiot.googleapis.com/overview?project=_
-[adc]: https://cloud.google.com/docs/authentication#developer_workflow
+[cloud-iot-api]: https://console.developers.google.com/iot
## Run the sample
