Merge branch '2.1.x' into 2.2.x

Closes gh-20042

Author: wilkinsona

spring-boot-project/spring-boot-parent/pom.xml

@@ -29,7 +29,7 @@
 		<maven.version>3.5.4</maven.version>
 		<maven-resolver.version>1.1.1</maven-resolver.version>
 		<spock.version>1.3-groovy-2.5</spock.version>
-		<spring-asciidoctor-extensions.version>0.3.0.RELEASE</spring-asciidoctor-extensions.version>
+		<spring-asciidoctor-extensions.version>0.4.0.RELEASE</spring-asciidoctor-extensions.version>
 		<spring-doc-resources.version>0.1.3.RELEASE</spring-doc-resources.version>
 		<spring-doc-resources.url>https://repo.spring.io/release/io/spring/docresources/spring-doc-resources/${spring-doc-resources.version}/spring-doc-resources-${spring-doc-resources.version}.zip</spring-doc-resources.url>
 		<testcontainers.version>1.12.5</testcontainers.version>