If you will look at the source code for the Privacy Browser 2.7.1 release, you will see that I have already followed the instructions you link to, although for the 2.8 release I am going to switch back to the older syntax because Android Studio complained it couldn’t find the 3.0.1 Gradle plugin with the google() syntax and recommended:
maven {
url 'https://maven.google.com'
}
Also, see this feature request that was supposed to add support for this, but apparently hasn’t in all cases.
The documentation I linked to previously is incomplete. This page has better instructions and shows that google() must be listed in both the buildscript and allprojects sections of the build.gradle file: