Use more naturally-sounding ensures

These match Basecamp and the existing predicate methods

app/controllers/admin_controller.rb

@@ -1,3 +1,3 @@
 class AdminController < ApplicationController
-  before_action :ensure_is_staff_member
+  before_action :ensure_staff
 end

app/controllers/concerns/authorization.rb

@@ -1,10 +1,10 @@
 module Authorization
   private
-    def ensure_can_administer
+    def ensure_admin
       head :forbidden unless Current.user.admin?
     end
 
-    def ensure_is_staff_member
+    def ensure_staff
       head :forbidden unless Current.user.staff?
     end
 end

app/controllers/webhooks/activations_controller.rb

@@ -1,5 +1,5 @@
 class Webhooks::ActivationsController < ApplicationController
-  before_action :ensure_can_administer
+  before_action :ensure_admin
   before_action :set_webhook
 
   def create

app/controllers/webhooks_controller.rb

@@ -1,5 +1,5 @@
 class WebhooksController < ApplicationController
-  before_action :ensure_can_administer
+  before_action :ensure_admin
   before_action :set_collection
   before_action :set_webhook, except: %i[ index new create ]