v.db.update: move layer number to required tab because column is required and dependent on layer

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@56511 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/v.db.update/v.db.update.py

@@ -24,6 +24,7 @@
 #%option G_OPT_V_MAP
 #%end
 #%option G_OPT_V_FIELD
+#% required: yes
 #%end
 #%option G_OPT_DB_COLUMN
 #% key: column