Fix source highlighting in reference documentation.

Tweak the declaration of the Asciidoctor build plugin to properly select highlight.js as source highlighter.

Fixes #1777.

Author: odrotbohm

parent/pom.xml

@@ -555,8 +555,8 @@
 										<sourceDocumentName>index.adoc</sourceDocumentName>
 										<backend>html5</backend>
 										<outputDirectory>${generated-docs.directory}</outputDirectory>
-										<sourceHighlighter>highlight.js</sourceHighlighter>
 										<attributes>
+											<source-highlighter>highlight.js</source-highlighter>
 											<highlightjsdir>js/highlight</highlightjsdir>
 											<highlightjs-theme>github</highlightjs-theme>
 											<linkcss>true</linkcss>