Fix deprecation warnings for Django 1.11 and Django 2.0.

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

mayan/apps/common/mixins.py

@@ -3,9 +3,9 @@ from __future__ import unicode_literals
 from django.conf import settings
 from django.contrib import messages
 from django.core.exceptions import PermissionDenied
-from django.core.urlresolvers import reverse
 from django.db.models.query import QuerySet
 from django.http import HttpResponseRedirect
+from django.urls import reverse
 from django.utils.translation import ungettext, ugettext_lazy as _
 
 from permissions import Permission