Async combine latest operator implementation for RxJava2 in Kotlin

asyncCombineLatestRxJava2.kt

fun <T1, T2, T3, R> asyncCombineLatest(o1: Observable<T1>,
                                       o2: Observable<T2>,
                                       o3: Observable<T3>,
                                       asyncCombineFunc: (T1, T2, T3) -> Observable<R>): Observable<R> =
        Observable.combineLatest(o1, o2, o3,
                Function3<T1, T2, T3, Observable<R>> { t1, t2, t3 -> asyncCombineFunc(t1, t2, t3) }
        ).flatMap { it }