FIX: resolved the sqrt(2) issue in denspeed.pyx
FIX: resolved the sqrt(2) issue in denspeed.pyx

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