Add missing drop of running column on ir.cron

issue2384

trytond/ir/cron.py

@@ -69,6 +69,7 @@ class Cron(ModelSQL, ModelView):
         table.column_rename('numbercall', 'number_calls')
         table.column_rename('doall', 'repeat_missed')
         table.column_rename('nextcall', 'next_call')
+        table.drop_column('running')
 
         super(Cron, self).init(module_name)