Fix bug in gem segmentation

compact/gem_tracker_endcap.xml

@@ -216,7 +216,7 @@
   <readouts>
     <readout name="GEMTrackerEndcapHits">
       <segmentation type="CartesianGridXZ" grid_size_x="50*um" grid_size_z="250*um" />
-      <id>system:8,barrel:2,layer:4,module:12,sensor:2,x:32:-16,y:-16</id>
+      <id>system:8,barrel:2,layer:4,module:12,sensor:2,x:32:-16,z:-16</id>
     </readout>
   </readouts>