I do not know if this is a limited time offer or not. I found this offer on Nov 7 , 2017 on the Gradle.org in the books section.
Book web site wrote:Android adopted Gradle as the preferred build automation system a few years ago, but many Android developers are still unfamiliar with this open source tool. This hands-on guide provides a collection of Gradle recipes to help you quickly and easily accomplish the most common build tasks for your Android apps. You’ll learn how to customize project layouts, add dependencies, and generate many different versions of your app.
Gradle is based on Groovy, yet very little knowledge of the JVM language is required for you to get started. Code examples use Android SDK version 23, with emulators from Marshmallow (Android 6) or Lollipop (Android 5). If you’re comfortable with Java and Android, you’re ready.
You can read more about this book here and offer here
“The strongest of all warriors are these two — Time and Patience.” ― Leo Tolstoy, War and Peace