Auto incrementing versionCode based on Jenkins build

build.gradle

android {
    defaultConfig {
    //..
        versionCode computeVersionCode()
        versionName computeVersionName()
   //..
    }
ext {
    versionMajor = 1
    versionMinor = 0
    versionPatch = 1

    jenkinsBuildNumber = Integer.valueOf(System.getenv().BUILD_NUMBER ?: 0)
}

def computeVersionName() {
    return "${versionMajor}.${versionMinor}.${versionPatch}"
}

def computeVersionCode() {
    return (versionMajor * 100_000) + (versionMinor * 10_000) + (versionPatch * 1_000) + jenkinsBuildNumber
}