Fix spell

sale.py

@@ -937,7 +937,7 @@ class SaleLine(ModelSQL, ModelView):
         super(SaleLine, self).__init__()
         self._order.insert(0, ('sequence', 'ASC'))
         self._error_messages.update({
-            'missing_account_revenue': 'It miss ' \
+            'missing_account_revenue': 'It misses ' \
                     'an "account_revenue" default property!',
             'customer_location_required': 'The customer location is required!',
             })
@@ -1547,7 +1547,7 @@ class Invoice(ModelSQL, ModelView):
         super(Invoice, self).__init__()
         self._error_messages.update({
             'delete_sale_invoice': 'You can not delete invoices ' \
-                    'that comes from a sale!',
+                    'that come from a sale!',
             'reset_invoice': 'You cannot reset to draft an invoice '\
                 'generated by a sale.',
             })