Fixes #318

• Upgrades commons-lang3 to 3.11
• Replaces invalid use of Pair with Maps.immutableEntry from Guava
• Reintroduce macOS GitHub Actions test
• Remove ZOS from Os because it throws errors (Apache Commons problem)

For users finding this issue and wanting to use gogradle on macOS right now, use the following buildscript:

buildscript {
    repositories {
        maven { url 'https://jitpack.io' }
    }
    dependencies {
        classpath 'com.github.doctorpangloss:gogradle:adae13ed1d'
    }
}

apply plugin: 'com.github.blindpirate.gogradle'

golang {
    packagePath = 'github.com/...'
}