frozen_string_literal, Coding standards fixed and ruby 2.7 warnings - redmine 4.1 and ruby 2.5 is required

db/migrate/001_create_messenger_settings.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class CreateMessengerSettings < ActiveRecord::Migration[4.2]
   def change
     create_table :messenger_settings do |t|

db/migrate/002_add_default_mentions.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AddDefaultMentions < ActiveRecord::Migration[4.2]
   def change
     add_column :messenger_settings, :default_mentions, :string

db/migrate/003_add_private_settings.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AddPrivateSettings < ActiveRecord::Migration[4.2]
   def change
     add_column :messenger_settings, :post_private_contacts, :integer, default: 0, null: false

db/migrate/004_add_direct_messages.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AddDirectMessages < ActiveRecord::Migration[4.2]
   def change
     add_column :messenger_settings, :messenger_direct_users_messages, :integer, default: 0, null: false