Minor typo in section 11, 'Display a user's books'

[ashleydb]

https://codelabs.developers.google.com/codelabs/cloud-nodejs/index.html?index=..%2F..%2Fcloud#10

Near the top of the page, section 11, 'Display a user's books', there is a 'books.js' code snippet. The 'books.js' heading has two github symbols in it.