README.md in backlog_kit-0.14.0 vs README.md in backlog_kit-0.15.0

@@ -96,10 +96,10 @@
 client = BacklogKit::Client.new
 ```
 
 ## Supported Backlog API Version
 
-BacklogKit supports Backlog API [2.8.0](http://developer.nulab-inc.com/docs/backlog/changes#ver_2.8.0).
+BacklogKit supports Backlog API [2.9.0](http://developer.nulab-inc.com/docs/backlog/changes#ver_2.9.0).
 
 BacklogKit's API documentation is [here](http://www.rubydoc.info/gems/backlog_kit).
 
 ## Supported Ruby Versions