Update gitbucket to 4.39.0

Author: scala-steward-bot

build.sbt

@@ -2,4 +2,4 @@ name := "gitbucket-helloworld-plugin"
 organization := "io.github.gitbucket"
 version := "1.0.0"
 scalaVersion := "2.13.10"
-gitbucketVersion := "4.38.4"
+gitbucketVersion := "4.39.0"