Fix spell

purchase.py

@@ -842,7 +842,7 @@ class PurchaseLine(ModelSQL, ModelView):
         self._order.insert(0, ('sequence', 'ASC'))
         self._error_messages.update({
             'supplier_location_required': 'The supplier location is required!',
-            'missing_account_expense': 'It miss ' \
+            'missing_account_expense': 'It misses ' \
                     'an "account_expense" default property!',
             })
 
@@ -1667,7 +1667,7 @@ class Invoice(ModelSQL, ModelView):
         super(Invoice, self).__init__()
         self._error_messages.update({
                 'delete_purchase_invoice': 'You can not delete invoices ' \
-                    'that comes from a purchase!',
+                    'that come from a purchase!',
                 'reset_invoice': 'You cannot reset to draft an invoice '\
                     'generated by a purchase.',
             })