fix python 2 compatible helpers for nested unicode (#58)

BUG FIXES:

- Fix python 2 compatible helpers for nested CJK charset

Author: ucloud-bot

tests/test_unit/test_core/test_encoder.py

@@ -13,6 +13,7 @@
         ({"foo": True}, {"foo": "true"}),
         ({"foo": False}, {"foo": "false"}),
         ({"IP": ["127.0.0.1"]}, {"IP.0": "127.0.0.1"}),
+        ({"TemplateParams": [u"中文"]}, {"TemplateParams.0": u"中文"}),
         ({"IP": ["foo", "bar"]}, {"IP.0": "foo", "IP.1": "bar"}),
         ({"IP": [{"foo": "bar"}]}, {"IP.0.foo": "bar"}),
     ],

ucloud/core/typesystem/encoder.py

@@ -1,3 +1,6 @@
+from ucloud.core.utils.compat import str
+
+
 def encode(d: dict) -> dict:
     result = {}