Make addErrorNotification raise a warning

Summary:
These are recoverable, handled errors. We shouldn't treat these
as events that require actions from us. They also have
a tendency of firing a lot.

Reviewed By: nikoant

Differential Revision: D26202358

fbshipit-source-id: 445f3c2bcd0041d5cd773ec04172fdeed9b32222

desktop/app/src/reducers/notifications.tsx

@@ -203,7 +203,7 @@ export function addErrorNotification(
   error?: any,
 ): Action {
   // TODO: use this method for https://github.com/facebook/flipper/pull/1478/files as well
-  console.error(title, message, error);
+  console.warn(title, message, error);
   return addNotification({
     client: null,
     pluginId: 'globalError',