BF - changed wrong nibabel import in doctest
BF - changed wrong nibabel import in doctest

This was cruft from copying optpkg from nibabel

maurozucchelli/dipy,JohnGriffiths/dipy,jyeatman/dipy,nilgoyyou/dipy,nilgoyyou/dipy,sinkpoint/dipy,rfdougherty/dipy,villalonreina/dipy,jyeatman/dipy,JohnGriffiths/dipy,rfdougherty/dipy,demianw/dipy,mdesco/dipy,demianw/dipy,sinkpoint/dipy,oesteban/dipy,samuelstjean/dipy,samuelstjean/dipy,beni55/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,StongeEtienne/dipy,Messaoud-Boudjada/dipy,oesteban/dipy,maurozucchelli/dipy,matthieudumont/dipy,FrancoisRheaultUS/dipy,Messaoud-Boudjada/dipy,beni55/dipy,villalonreina/dipy,StongeEtienne/dipy,maurozucchelli/dipy,samuelstjean/dipy,mdesco/dipy