Actually use the right exception class.

Two HTTPError classes exist. Need to use the one in notifications_python_client.

app/main/views/templates.py

@@ -7,7 +7,7 @@ from dateutil.parser import parse
 
 from notifications_utils.template import Template
 from notifications_utils.recipients import first_column_heading
-from notify_client import HTTPError
+from notifications_python_client.errors import HTTPError
 
 from app.main import main
 from app.utils import user_has_permissions

tests/app/main/views/test_templates.py

@@ -5,7 +5,7 @@ import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
 from freezegun import freeze_time
-from notify_client import HTTPError
+from notifications_python_client.errors import HTTPError
 
 from tests import validate_route_permission, template_json, single_notification_json
 from app.main.views.templates import get_last_use_message, get_human_readable_delta

tests/conftest.py

@@ -20,7 +20,7 @@ from app.notify_client.models import (
     InvitedUser
 )
 
-from notify_client.errors import HTTPError
+from notifications_python_client.errors import HTTPError
 
 
 @pytest.fixture(scope='session')