Fix easy rubocop issues

lib/spree/core/environment/calculators.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Spree
   module Core
     class Environment
@@ -9,4 +11,3 @@ module Spree
     end
   end
 end
-

lib/spree/core/environment_extension.rb

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module Spree
   module Core
     module EnvironmentExtension
       extend ActiveSupport::Concern
 
       def add_class(name)
-        self.instance_variable_set "@#{name}", Set.new
+        instance_variable_set "@#{name}", Set.new
 
         create_method( "#{name}=".to_sym ) { |val|
           instance_variable_set( "@" + name, val)
@@ -17,9 +19,9 @@ module Spree
 
       private
 
-        def create_method(name, &block)
-          self.class.send(:define_method, name, &block)
-        end
+      def create_method(name, &block)
+        self.class.__send__(:define_method, name, &block)
+      end
     end
   end
 end

lib/spree/i18n/base.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Spree
   module ViewContext
     def self.context=(context)

lib/spree/i18n/initializer.rb

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