fix FutureWarning

[nhsavage]

fix these warnings:

FutureWarning: In a future version of xarray the default value for coords will change from coords='different' to coords='minimal'. This is likely to lead to different results when multiple datasets have matching variables with overlapping values. To opt in to new defaults and get rid of these warnings now use `set_options(use_new_combine_kwarg_defaults=True) or set coords explicitly.

rasied from pycpt_convert.py:455, compute_scores_func.py

[Eleanor-Dean]

closing this to expand now into a bigger issue