Align bootJar example with changes to Asciidoctor's Gradle plugin

Signed-off-by: Jens Teglhus Møller <jtm@mostlyharmless.dk>

See gh-962

docs/src/docs/asciidoc/getting-started.adoc

@@ -179,7 +179,7 @@ If you are not using Spring Boot and its plugin management, declare the plugin w
 ----
 	bootJar {
 		dependsOn asciidoctor <1>
-		from ("${asciidoctor.outputDir}/html5") { <2>
+		from ("${asciidoctor.outputDir}") { <2>
 			into 'static/docs'
 		}
 	}