Fix some easy rubocop issues

lib/spree/core.rb

@@ -35,7 +35,7 @@ module Spree
   #
   # This method is defined within the core gem on purpose.
   # Some people may only wish to use the Core part of Spree.
-  def self.config(&block)
+  def self.config
     yield(Spree::Config)
   end
 end

lib/spree/core/calculated_adjustments.rb

@@ -65,15 +65,15 @@ module Spree
             calculator.compute(calculable)
           end
 
-          private
-
           def self.model_name_without_spree_namespace
             to_s.tableize.gsub('/', '_').sub('spree_', '')
           end
+          private_class_method :model_name_without_spree_namespace
 
           def self.spree_calculators
             Rails.application.config.spree.calculators
           end
+          private_class_method :spree_calculators
         end
       end
     end

lib/spree/core/delegate_belongs_to.rb

@@ -91,4 +91,4 @@ module DelegateBelongsTo
   protected :delegator_for
 end
 
-ActiveRecord::Base.__send__(:include, DelegateBelongsTo)
+ActiveRecord::Base.include(DelegateBelongsTo)

lib/spree/core/permalinks.rb

@@ -71,5 +71,5 @@ module Spree
   end
 end
 
-ActiveRecord::Base.__send__ :include, Spree::Core::Permalinks
-ActiveRecord::Relation.__send__ :include, Spree::Core::Permalinks
+ActiveRecord::Base.include(Spree::Core::Permalinks)
+ActiveRecord::Relation.include(Spree::Core::Permalinks)

lib/spree/i18n/initializer.rb

@@ -1,3 +1,3 @@
 # frozen_string_literal: true
 
-Spree::BaseController.__send__(:include, Spree::ViewContext)
+Spree::BaseController.include(Spree::ViewContext)