error in CI with `test_setBatchCoregistrationFmap`

[Remi-Gau]

error in CI witrh test_setBatchCoregistrationFmap

failure: unique: X must be an array or cell array of strings

  unique:52 (/usr/share/octave/4.2.2/m/set/unique.m)

  query:155 (/home/travis/build/cpp-lln-lab/CPP_SPM/lib/bids-matlab/+bids/query.m)

  setBatchCoregistrationFmap:38 (/tmp/oct-Psk2Gg/batches/setBatchCoregistrationFmap.m)

  test_setBatchCoregistrationFmap>test_setBatchCoregistrationFmapBasic:21 (/home/travis/build/cpp-lln-lab/CPP_SPM/tests/test_setBatchCoregistrationFmap.m)

Originally posted by @Remi-Gau in #240 (comment)

[Remi-Gau]

fixed as part of #367