You can use install it via NPM:

$ npm install gitbook-plugin-ga

And use it for your book with in the book.json:

{
 "plugins": ["ga"]
}

You can set the Google Analytics tracking ID using the plugins configuration in the book.json:

{
 "plugins": ["ga"],
 "pluginsConfig": {
 "ga": {
 "token": "UA-XXXX-Y"
 }
 }
}

You can customize the tracker object by passing additional configuration options. You can either pass in auto, none or an object:

{
 "plugins": ["ga"],
 "pluginsConfig": {
 "ga": {
 "token": "UA-XXXX-Y",
 "configuration": {
 "cookieName": "new_cookie_name",
 "cookieDomain": "mynew.domain.com"
 }
 }
 }
}

For an overview of all available configuration parameters, please refer to the analytics.js field reference.