AppVeyor: unpin gdal et al
AppVeyor: unpin gdal et al

tomalrussell/smif,nismod/smif,nismod/smif,willu47/smif,willu47/smif,willu47/smif,nismod/smif,tomalrussell/smif,tomalrussell/smif,willu47/smif,tomalrussell/smif,nismod/smif