code: public static <T> FlowableTransformer<T, List<T>> buffer(final int maxSize, final long duration,
              final TimeUnit unit) {
          return buffer(maxSize, Functions.constant(duration), unit);
      }
docs: Buffers the source {@link Flowable} into {@link List}s, emitting Lists when
  the size of a list reaches {@code maxSize} or if the elapsed time since last
  emission from the source reaches the given duration.
  {@link Schedulers#computation} is used for scheduling an inserted emission.
  
  @param maxSize
  max size of emitted lists
  @param duration
  buffered list is emitted if the elapsed time since last emission
  from the source reaches this duration
  @param unit
  unit of {@code duration}
  @param <T>
  type of the source stream items
  @return source with operator applied