Cancel button on new book page doesn't go back to bookshelf #1662

Describe the bug
If you are in a bookshelf and creating a new book, clicking the cancel button always brings you back to the "books" page, instead of back to the bookshelf you had open.

Steps To Reproduce
Steps to reproduce the behavior:

1. Go to a bookshelf (https://demo.bookstackapp.com/shelves/an-example-bookshelf)
2. Click "New Book" on the right hand side. This brings you to the create-book page within the bookshelf (https://demo.bookstackapp.com/shelves/an-example-bookshelf/create-book)
3. Click the "Cancel" button.

Expected behavior
Upon clicking the cancel button, I would expect to be brought back to the bookshelf I had open (https://demo.bookstackapp.com/shelves/an-example-bookshelf).

Actual behavior
You are redirected to the "Books" page (https://demo.bookstackapp.com/books).

Your Configuration (please complete the following information):

• Exact BookStack Version (Found in settings): 0.27.4
• PHP Version: 7.2.22
• Hosting Method (Nginx/Apache/Docker): nginx/1.12.2 on CentOS 7

Additional context
The configuration info is for my install, but the steps to reproduce include URLs from the demo (which is running 0.27.3) for ease of use.
This is definitely not a huge deal, but it's a little annoying so I figured I would report it.