Update Content-Type on Dyn Client Registration doc (#6256)
Update Content-Type on Dyn Client Registration doc (#6256)

Using `client/json` against API2, the service replies with
```
{"statusCode":415,"error":"Unsupported Media Type","message":"Unsupported Media Type"}
```
jeffreylees/docs,jeffreylees/docs,yvonnewilson/docs,jeffreylees/docs,yvonnewilson/docs,yvonnewilson/docs,auth0/docs,auth0/docs,auth0/docs