Fix lack of syntax highlighting when using Maven

See gh-620

Author: gavvvr

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

@@ -100,7 +100,7 @@ the configuration are described below.
 			<plugin> <2>
 				<groupId>org.asciidoctor</groupId>
 				<artifactId>asciidoctor-maven-plugin</artifactId>
-				<version>1.5.3</version>
+				<version>1.5.8</version>
 				<executions>
 					<execution>
 						<id>generate-docs</id>

samples/rest-notes-spring-data-rest/pom.xml

@@ -72,7 +72,7 @@
 			<plugin>
 				<groupId>org.asciidoctor</groupId>
 				<artifactId>asciidoctor-maven-plugin</artifactId>
-				<version>1.5.3</version>
+				<version>1.5.8</version>
 				<executions>
 					<execution>
 						<id>generate-docs</id>