buildscript {
    ext.kotlin_version = '1.2.30'
    ext.lifecycle_version = '1.1.1'
    ext.retrofit_version = '2.4.0'
    ext.dagger2_version = '2.16'
    ext.android_support_version = '28.0.0-alpha3'
    ext.room_version = '1.1.1'

    // ...
}