set the classpath in project level build.gradle file for Gradle Play Publisher Plugin

build.gradle

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
        classpath 'com.github.triplet.gradle:play-publisher:1.1.5 //add the classpath for Gradle Play Publisher Plugin
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}