Add support (and fix bug) for Python 3.7

tests/test_utils.py

@@ -91,3 +91,9 @@ class PillarUtilsTests(unittest.TestCase):
 
         self.assertFalse(utils.is_valid_id(u'55f…'))
         self.assertFalse(utils.is_valid_id(u'ประเทศไทย'))
+
+    def test_join_api_me(self):
+        # This reproduces an issue we saw when upgrading to Python 3.7.
+        # It resulted in the '/users/me' part being doubled.
+        the_url = utils.join_url('https://cloud.blender.org/api/', '/users/me')
+        self.assertEqual('https://cloud.blender.org/api/users/me', the_url)