PEP8 cleanups

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/navigation/classes.py

@@ -16,6 +16,7 @@ from django.template.defaulttags import URLNode
 from django.urls import resolve, reverse
 from django.utils.encoding import force_str, force_text
 from django.utils.module_loading import import_string
+from django.utils.translation import ugettext_lazy as _
 
 from mayan.apps.common.literals import (
     TEXT_SORT_FIELD_PARAMETER, TEXT_SORT_FIELD_VARIABLE_NAME,