replace except: pass with suppress() context manager

src/c3nav/urls.py

@@ -1,3 +1,5 @@
+from contextlib import suppress
+
 from django.conf import settings
 from django.conf.urls import include, url
 from django.contrib import admin
@@ -15,8 +17,6 @@ urlpatterns = [
 ]
 
 if settings.DEBUG:
-    try:
+    with suppress(ImportError):
         import debug_toolbar
         urlpatterns.insert(0, url(r'^__debug__/', include(debug_toolbar.urls)))
-    except ImportError:
-        pass