chore(ingress): Fix example usage in docs to match new YAML

We changed the helm charts for this, just updating docs to match

Non breaking change.

Author: krisnova

charts/workflow/values.yaml

@@ -117,7 +117,7 @@ controller:
   #
   # This will be the hostname that is used to build endpoints such as "deis.$HOSTNAME"
   platform_domain: ""
-  
+
 database:
   # The username and password to be used by the on-cluster database.
   # If left empty they will be generated using randAlphaNum

src/installing-workflow/experimental-native-ingress.md

@@ -5,7 +5,7 @@
 Now that Helm is installed and the repository has been added, install Workflow with a native ingress by running:
 
 ```
-$ helm install deis/workflow --namespace deis --set experimental_native_ingress=true,global.hostname="deis.com"
+$ helm install deis/workflow --namespace deis --set global.experimental_native_ingress=true,controller.platform_domain=deis.com
 ```
 
 Where `global.hostname` is a **required** parameter that is traditionally not required for Workflow. In this example we are using `deis.com` for `$hostname`.