DOC: corrected doctest
DOC: corrected doctest

StongeEtienne/dipy,JohnGriffiths/dipy,matthieudumont/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy,StongeEtienne/dipy,JohnGriffiths/dipy,matthieudumont/dipy