rubocop corrections

app/controllers/books_controller.rb

@@ -1,26 +1,25 @@
+# frozen_string_literal: true
+
+# Books controller
 class BooksController < ApplicationController
-  before_action :set_book, only: [:show, :edit, :update, :add_to_cart]
-  before_action :ensure_admin, only: [:edit, :update]
+  before_action :set_book, only: %i[show edit update add_to_cart]
+  before_action :ensure_admin, only: %i[edit update]
 
   def index
-    if current_user&.admin?
-      books = Book.all
-    else
-      books = Book.published
-    end
+    books = if current_user&.admin?
+              Book.all
+            else
+              Book.published
+            end
     @books = books.map { |book| BooksPresenter.new(book) }
   end
 
-  def show
-  end
+  def show; end
 
-  def edit
-  end
+  def edit; end
 
   def update
-    if @book.update(book_params)
-      redirect_to '/books'
-    end
+    redirect_to '/books' if @book.update(book_params)
   end
 
   def add_to_cart