code: static <T> MaybeObserver<T> wrap(MaybeObserver<T> downstream,
                                       List<RunnableInstrumenter> instrumentations) {
          return new RxInstrumentedMaybeObserver<>(downstream, instrumentations);
      }
docs: Wrap a observer.
  @param downstream The downstream observer
  @param instrumentations The instrumentations
  @param <T> The type
  @return The wrapped subscriber