Updated _data.py fixing validateDataItem()
Updated _data.py fixing validateDataItem()

Was `/ validateDataItem` which is invalid url - this function could never be run successfully; changed to `/validateDataItem`. Works correctly after that.
DShokes/ArcREST,pLeBlanc93/ArcREST,BrunoCaimar/ArcREST,adegwerth/ArcREST,Esri/ArcREST