DOC: Minor changes multi shell -> multi-shell
DOC: Minor changes multi shell -> multi-shell

sinkpoint/dipy,villalonreina/dipy,nilgoyyou/dipy,demianw/dipy,nilgoyyou/dipy,matthieudumont/dipy,StongeEtienne/dipy,jyeatman/dipy,JohnGriffiths/dipy,StongeEtienne/dipy,oesteban/dipy,demianw/dipy,sinkpoint/dipy,JohnGriffiths/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,jyeatman/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,oesteban/dipy