code: public <B> ReaderT<W,T,B> mapFn(final Function<? super R, ? extends B> f) {
          return new ReaderT<W,T,B>(
                                    run.map(o -> o.mapFn(f)));
      }
docs: Map the wrapped Future
  
  <pre>
  {@code
  FutureT.of(AnyM.fromStream(Arrays.asFuture(10))
  .map(t->t=t+1);
  
  
  //FutureT<AnyMSeq<Stream<Future[11]>>>
  }
  </pre>
  
  @param f Mapping function for the wrapped Future
  @return FutureT that applies the transform function to the wrapped Future