fix wrong attribute name in template

fixes http://api3.geo.admin.ch/1410241912/rest/services/ech/MapServer/ch.swisstopo.geologie-geocover/607526/htmlPopup?imageDisplay=1624,1028,96&lang=de&mapExtent=583557.0155328292,191761.06718554336,587617.0155328292,194331.06718554336