...
allprojects {
    repositories {
        google()      // <--- add this line at the beginning (to avoid 'Could not resolve all files for configuration ':app:debugCompileClasspath'.' error)
        mavenLocal()
        jcenter()
        maven {
            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
            url "$rootDir/../node_modules/react-native/android"
        }
    }
}

task wrapper(type: Wrapper) {
    gradleVersion = '4.4'
    distributionUrl = distributionUrl.replace("bin", "all")
}