DateTimeSpan not calculating correctly

[ferdyrod]

Hi,

I'm doing some testing with the DateTimeSpan class and I've been having some issues with the calculations.

if a have the following

    val startDate = DateTime.fromString("Mon, 01 Jan 2019 00:00:00 UTC").local
    val endDate = DateTime.fromString("Sat, 01 Sep 2019 00:00:00 UTC").local
    val span = (startDate until endDate).span

    assertEquals("8", span.totalMonths)  //Fails due to span calculation being '7M 4W 3D'

It fails because it's not calculating the 8 months difference there is between the two dates.