fix: django.utils.six not available before django 1.6

jsignature/widgets.py

@@ -9,6 +9,7 @@ from django.template.loader import render_to_string
 from django.forms.widgets import HiddenInput
 from django.core import validators
 from django.core.exceptions import ValidationError
+
 from django.utils.safestring import mark_safe
 from django.utils.translation import ugettext_lazy as _
 from jsignature.settings import JSIGNATURE_DEFAULT_CONFIG