[FIX] contract: Delete cascade line wizard

For avoiding problems while trying to remove the contract/contract line

contract/__manifest__.py

@@ -9,7 +9,7 @@
 
 {
     'name': 'Recurring - Contracts Management',
-    'version': '12.0.6.0.2',
+    'version': '12.0.6.0.3',
     'category': 'Contract Management',
     'license': 'AGPL-3',
     'author': "OpenERP SA, "

contract/wizards/contract_line_wizard.py

@@ -25,6 +25,7 @@ class ContractLineWizard(models.TransientModel):
         string="Contract Line",
         required=True,
         index=True,
+        ondelete="cascade",
     )
 
     @api.multi