Fix Rubocop offenses

Author: MrSerth

app/controllers/collections_controller.rb

@@ -117,7 +117,7 @@ def save_shared # rubocop:disable Metrics/AbcSize
   end
 
   def leave
-    if @collection.users.count == 1
+    if @collection.users.one?
       @collection.destroy
       redirect_to Collection, notice: t('common.notices.object_deleted', model: Collection.model_name.human)
     else

app/models/user.rb

@@ -121,7 +121,7 @@ def handle_group_memberships
 
   def handle_collection_membership
     collections.each do |collection|
-      collection.destroy if collection.users.count == 1
+      collection.destroy if collection.users.one?
     end
   end
 

app/policies/application_policy.rb

@@ -41,7 +41,7 @@ def admin?
     @user.present? && @user.role == 'admin'
   end
 
-  def everyone
+  def everyone # rubocop:disable Naming/PredicateMethod
     # `everyone` here means `every user logged in`
     @user.present?
   end