backward compatibility django shim

Author: mattip

codespeed/models.py

@@ -9,7 +9,11 @@
 from django.urls import reverse
 from django.conf import settings
 from django.db import models
-from django.utils.encoding import python_2_unicode_compatible
+try:
+    from django.utils.encoding import python_2_unicode_compatible
+except ImportError:
+    def python_2_unicode_compatible(arg):
+        return arg
 
 from .commits.github import GITHUB_URL_RE