Update "display name" --> "title" for integration errors (#7854)

Related to https://github.com/mattermost/mattermost-webapp/pull/308

i18n/en.json

@@ -4436,7 +4436,7 @@
   },
   {
     "id": "model.command.is_valid.display_name.app_error",
-    "translation": "Invalid display name"
+    "translation": "Invalid title"
   },
   {
     "id": "model.command.is_valid.id.app_error",
@@ -4896,7 +4896,7 @@
   },
   {
     "id": "model.incoming_hook.display_name.app_error",
-    "translation": "Invalid display name"
+    "translation": "Invalid title"
   },
   {
     "id": "model.incoming_hook.id.app_error",
@@ -4988,7 +4988,7 @@
   },
   {
     "id": "model.outgoing_hook.is_valid.display_name.app_error",
-    "translation": "Invalid display name"
+    "translation": "Invalid title"
   },
   {
     "id": "model.outgoing_hook.is_valid.id.app_error",