How to extend cordova build.gradle to change repositories

Problem

Due to a problem with jcenter repository I need to instruct gradle to use use maven repository. I could fix the problem changing the file build.gradle:

Original:

//...
buildscript {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com"
        }
    }
    //...
}
allprojects {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com"
        }
    }
}
//...

Modified:

//...
buildscript {
    repositories {
        mavenCentral()
        maven {
            url "https://maven.google.com"
        }
        jcenter()
    }
    //...
}
allprojects {
    repositories {
        mavenCentral()
        maven {
            url "https://maven.google.com"
        }
        jcenter()
    }
}
//...

Since this file is not versioned, and per Cordova documentation, the way to extend build.gradle is to create a build-extras.gradle file, I've done so and have tried to add the same content I've modified in the build.gradle file, like:

build-extras.gradle

buildscript {
    repositories {
        mavenCentral()
        maven {
            url "https://maven.google.com"
        }
        jcenter()
    }
    //...
}
allprojects {
    repositories {
        mavenCentral()
        maven {
            url "https://maven.google.com"
        }
        jcenter()
    }
}

Question

To sum up, changing the build.gradle file works but placing the same diffed content in build-extras.gradle it does not. Is there something that I'm missing?