GH-6 - Fix syntax highlighting in reference docs.

Switch to the correct attribute to set to enable this.

pom.xml

@@ -335,8 +335,8 @@ limitations under the License.
 										<sourceDirectory>${generated-asciidoc-sources.directory}</sourceDirectory>
 										<sourceDocumentName>index.adoc</sourceDocumentName>
 										<outputDirectory>${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>