build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'

        classpath 'com.novoda:bintray-release:0.8.0'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
    tasks.withType(Javadoc) {
        options.addStringOption('Xdoclint:none', '-quiet')
        options.addStringOption('encoding', 'UTF-8')
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}
task javadoc(type: Javadoc) {
    excludes = ['**/*.kt'] // < ---- Exclude all kotlin files from javadoc file.
    // ...
}