Update README.MD

Author: takezoe

README.MD

@@ -31,7 +31,7 @@ Plugin version | GitBucket version
 
 - Open a shell window at the root of the project, hit `sbt package`
 - if you update `gitbucket-announce-plugin`, remove any existing previous copy of `gitbucket-announce-plugin` from GITBUCKET_HOME/plugins
-- Copy target/scala-2.11/gitbucket-announce-plugin_2.11-X.X.jar into GITBUCKET_HOME/plugins
+- Copy target/scala-2.12/gitbucket-announce-plugin_2.12-X.X.jar into GITBUCKET_HOME/plugins
 - Restart GitBucket
 
 ## Release Notes