Add glt doctest.

[tsalo]

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Fixes # .

Changes proposed in this pull request

[codecov-io]

Codecov Report

Merging #2086 into master will increase coverage by 0.01%.
The diff coverage is 83.92%.

@@ Coverage Diff @@ ## master #2086 +/- ## ========================================== + Coverage 72.13% 72.15% +0.01%  ========================================== Files 1138 1139 +1 Lines 57271 57327 +56 Branches 8207 8212 +5 ========================================== + Hits 41313 41362 +49  - Misses 14665 14671 +6  - Partials 1293 1294 +1

Flag	Coverage Δ
#smoketests	72.15% <83.92%> (+0.01%)	⬆️
#unittests	69.76% <83.92%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
nipype/interfaces/afni/__init__.py	100% <100%> (ø)	⬆️
nipype/interfaces/afni/model.py	83.63% <83.63%> (ø)
nipype/interfaces/base.py	83.8% <0%> (+0.18%)	⬆️

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