Corrects az role assignment command

Author: Steven Smith

modules/installation-azure-service-principal.adoc

@@ -222,8 +222,8 @@ If you limit the service principal scope of the {product-title} installation pro
 [source,terminal]
 ----
 $ az role assignment create --role "User Access Administrator" \
-    --assignee-object-id $(az ad sp list --filter "appId eq '<appId>'" \ <1>
-       | jq '.[0].objectId' -r)
+    --assignee-object-id $(az ad sp list --filter "appId eq '<appId>'" \
+       | jq '.[0].id' -r)
 ----
 <1> Replace `<appId>` with the `appId` parameter value for your service principal.