Raise the minimum supported version of AsciidoctorJ to 2.5

Closes gh-751

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

@@ -83,7 +83,7 @@
 			<plugin>
 				<groupId>org.asciidoctor</groupId>
 				<artifactId>asciidoctor-maven-plugin</artifactId>
-				<version>1.5.8</version>
+				<version>2.2.1</version>
 				<executions>
 					<execution>
 						<id>generate-docs</id>
@@ -96,9 +96,6 @@
 							<doctype>book</doctype>
 							<logHandler>
 								<outputToConsole>true</outputToConsole>
-								<failIf>
-									<severity>DEBUG</severity>
-								</failIf>
 							</logHandler>
 						</configuration>
 					</execution>