Fix typo Cusom -> Custom (#279)

Author: apupier

documentation/modules/setup/pages/minikube.adoc

@@ -50,7 +50,7 @@ minikube -p {tutorial-namespace} addons enable registry
 
 == Install Knative
 
-=== Deploy Cusom Resource Definitions
+=== Deploy Custom Resource Definitions
 
 [.console-input]
 [source,bash,subs="+macros,+attributes"]
@@ -387,4 +387,4 @@ The https://github.com/ahmetb/kubens[kubens] utility installed as part of https:
 kubens {tutorial-namespace}
 ----
 
-=====
+=====