Fix issue #169 (force_text depracated)

Author: soomy

martor/utils.py

@@ -2,7 +2,7 @@
 from __future__ import unicode_literals
 
 from django.utils.functional import Promise
-from django.utils.encoding import force_text
+from django.utils.encoding import force_str
 from django.core.serializers.json import DjangoJSONEncoder
 
 import markdown
@@ -56,5 +56,5 @@ class LazyEncoder(DjangoJSONEncoder):
 
     def default(self, obj):
         if isinstance(obj, Promise):
-            return force_text(obj)
+            return force_str(obj)
         return super(LazyEncoder, self).default(obj)