Handle both admin and not admin usages

jsignature/fields.py

@@ -14,12 +14,12 @@ from .forms import (
 
 try:
     from django.utils import six
+
     string_types = six.string_types
 except ImportError:
     string_types = str
 
 
-
 class JSignatureField(models.Field):
     """
     A model field handling a signature captured with jSignature