Update Docbook Reference Plugin

build.gradle

@@ -10,7 +10,7 @@ buildscript {
 		classpath("org.gradle.api.plugins:gradle-tomcat-plugin:1.2.5")
 		classpath('me.champeau.gradle:gradle-javadoc-hotfix-plugin:0.1')
 		classpath('org.asciidoctor:asciidoctor-gradle-plugin:1.5.1')
-		classpath("io.spring.gradle:docbook-reference-plugin:0.3.0")
+		classpath("io.spring.gradle:docbook-reference-plugin:0.3.1")
 	}
 }