dev@locazia: fix User.json_format date fields

app/core/models/user/display_mixin.py

@@ -6,6 +6,6 @@ class DisplayMixin:
             "username": self.username,
             "lang_code": self.lang_code,
             "meta": self.meta,
-            "last_use": self.last_use,
-            "created": self.created
+            "last_use": self.last_use.isoformat(),
+            "created": self.created.isoformat()
         }