test: add test for make_json_safe() with uuid value

whoops, missed that..

tests/test_util.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8; -*-
 
 import json
+import uuid as _uuid
 from unittest import TestCase
 from unittest.mock import patch, MagicMock
 
@@ -564,6 +565,11 @@ class TestMakeJsonSafe(TestCase):
         value = mod.make_json_safe(person, key='person')
         self.assertEqual(value, "Betty Boop")
 
+    def test_uuid(self):
+        uuid = _uuid.uuid4()
+        value = mod.make_json_safe(uuid)
+        self.assertEqual(value, uuid.hex)
+
     def test_dict(self):
         model = self.app.model
         person = model.Person(full_name="Betty Boop")