README.md in fluent-plugin-bigquery-0.3.3 vs README.md in fluent-plugin-bigquery-0.3.4

@@ -12,9 +12,12 @@
   * https://developers.google.com/bigquery/loading-data-into-bigquery
 
 Current version of this plugin supports Google API with Service Account Authentication, but does not support
 OAuth flow for installed applications.
 
+## Notice
+If you use ruby-2.1 or earlier, you must use activesupport-4.2.x or earlier.
+
 ## Configuration
 
 ### Options
 
 | name                                   | type          | required?                   | default                                                | description                                                                                                          |