Diff order fix

[pdurham2]

Corrected issue where the diff order was hard coded as 2 in lad_filtering. Also added test_lad_filtering_scoring_diff_order to test_models which uses the last data points, takes the appropriate diff, and then compares to the adjusted actual to make sure the appropriate diff order is applied.

Related Issue: #120
@sayanchk for review

[sayanchk]

Looks good to me. Nice to have a unit test to test the diff_order.

Great work @pdurham2 ! Thanks for contributing to Luminaire!

[sayanchk]

@shahsmit14 Changes are approved. This is an important bug fix addressing a prediction bias issue under higher order differencing for the filtering model and should improve the model performance. This should go as a part of the next patch.

[shahsmit14]

@sayanchk If we want this to be released, we need the update for the version in setup.py.
@pdurham2 - Can you also add that in the same PR? new version will be 0.4.2 and the file to update will be https://github.com/zillow/luminaire/blob/master/setup.py#L17

[shahsmit14]

I'm just going to merge this and create a release MR.

[shahsmit14]

now available in https://pypi.org/project/luminaire/0.4.2/