[MRG+1] Fix issue 191

[tgsmith61591]

Description

The translated R code for the OCSB test included a if max_lag == 0, which has special meaning in R, since it's 1-indexed, not 0-indexed. We need to check for <= 0 in order to fix #191.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change

How Has This Been Tested?

Added a new unit test in pmdarima/arima/tests/test_arima.py

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[aaronreidsmith]

LGTM!