[FIX] contract: add missing dependency in computed field

contract/models/contract_line.py

@@ -479,6 +479,7 @@ class ContractLine(models.Model):
         'recurring_rule_type',
         'recurring_interval',
         'date_end',
+        'recurring_next_date',
     )
     def _compute_next_period_date_end(self):
         for rec in self: