Fix typo in field name date_send -> date_sent

issue2551

trytond/res/request.py

@@ -135,7 +135,7 @@ class Request(ModelSQL, ModelView):
             request_history_obj.create(values)
         self.write(ids, {
             'state': 'waiting',
-            'date_send': datetime.datetime.now(),
+            'date_sent': datetime.datetime.now(),
             })
 
     @ModelView.button