Change "is" check for 'GCV'

[mattcieslak]

This is causing an error in python 3.7

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@78f74e8). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #1769   +/-   ##
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  Coverage          ?   83.88%           
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  Files             ?      120           
  Lines             ?    14572           
  Branches          ?     2295           
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  Hits              ?    12224           
  Misses            ?     1824           
  Partials          ?      524

Impacted Files	Coverage Δ
dipy/reconst/mapmri.py	90.33% <100%> (ø)

[arokem]

Hey @mattcieslak - thanks for fixing this. Under what circumstances do you see this raising an error in Python 3.7? Is this something not currently covered by tests?

[mattcieslak]

It works in tests, but the string that ends up being compared in my code comes from a traits.Str object (https://github.com/PennBBL/qsiprep/blob/master/qsiprep/interfaces/dipy.py#L216), so checking the address using is doesn't work. Using == will convert it to a string and works.

[arokem]

OK. I figure it's a small change and since it sounds like testing it would be more than we need, I'm just going to go ahead and merge this.