rubocop: fix various Rubocop warnings.

app/models/user_feedback.rb

@@ -1,11 +1,12 @@
 class UserFeedback < ApplicationRecord
   self.table_name = "user_feedback"
 
+  attr_accessor :disable_dmail_notification
+
   belongs_to :user
   belongs_to :creator, class_name: "User"
-  attr_accessor :disable_dmail_notification
-  validates_presence_of :body, :category
-  validates_inclusion_of :category, :in => %w(positive negative neutral)
+  validates :body, presence: true
+  validates :category, presence: true, inclusion: { in: %w[positive negative neutral] }
   after_create :create_dmail, unless: :disable_dmail_notification
   after_update(:if => ->(rec) { CurrentUser.id != rec.creator_id}) do |rec|
     ModAction.log(%{#{CurrentUser.user.name} updated user feedback for "#{rec.user.name}":#{Routes.user_path(rec.user)}}, :user_feedback_update)