Add missing import

JIRA: FOR-523

lms/djangoapps/django_comment_client/forum/views.py

@@ -6,6 +6,7 @@ from django.contrib.auth.decorators import login_required
 from django.http import Http404
 from django.core.context_processors import csrf
 from django.contrib.auth.models import User
+from django.utils.translation import ugettext as _
 from django.views.decorators.http import require_GET
 import newrelic.agent