rubocop corrections

app/helpers/application_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module ApplicationHelper
 end

app/helpers/books_helper.rb

@@ -1,7 +1,10 @@
+# frozen_string_literal: true
+
 module BooksHelper
   def cart_summary
-    number_to_currency(@books.map{ |b| b.price }.reduce(:+))
+    number_to_currency(@books.map(&:price).reduce(:+))
   end
+
   def can_book_be_added?(book)
     logged_in? && book.quantity.positive? && !current_user.books.exists?(book.id)
   end

app/helpers/sessions_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module SessionsHelper
 end

app/helpers/users_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module UsersHelper
 end