Hmm, it wasn't working for me with the newest Gradle version.
Even when “useProguard false” was set I still saw my apk was obfuscated. So like Xavier Rubio Jansana suggested adding Proguard rule with one flag (dontobfuscate) worked for me.

buildTypes {
    debug {
        versionNameSuffix "-DEBUG"
        applicationIdSuffix ".debug"
        testCoverageEnabled true
        debuggable true
        minifyEnabled true
        shrinkResources false
        useProguard false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro', 'proguard-rules-without-obfuscation.pro'
    }
    release {
        debuggable false
        minifyEnabled true
        shrinkResources true
        zipAlignEnabled true
        useProguard true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}