v.centroids: add missing gispropmt for 'layer'

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@34672 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/v.centroids/v.centroids.py

@@ -47,6 +47,7 @@
 #% key: layer
 #% type: integer
 #% description: Layer number
+#% gisprompt: old_layer,layer,layer
 #% answer: 1
 #% required: no
 #%end