Add PLAN_LIMIT for now

Should remove this and make it something else

src/boxerror.js

@@ -52,6 +52,7 @@ BoxError.NGINX_ERROR = 'Nginx Error';
 BoxError.NOT_FOUND = 'Not found';
 BoxError.NOT_SIGNED = 'Not Signed';
 BoxError.OPENSSL_ERROR = 'OpenSSL Error';
+BoxError.PLAN_LIMIT = 'Plan Limit';
 BoxError.TASK_ERROR = 'Task Error';
 BoxError.TRY_AGAIN = 'Try Again';
 BoxError.UNKNOWN_ERROR = 'Unknown Error'; // only used for porting