Test Asciidoctor extension against AsciidoctorJ 2.2, 2.3, and 2.4

Closes gh-694

gradle.properties

@@ -4,4 +4,7 @@ asciidoctorj16Version=1.6.2
 javaFormatVersion=0.0.15
 asciidoctorj20Version=2.0.0
 asciidoctorj21Version=2.1.0
+asciidoctorj22Version=2.2.0
+asciidoctorj23Version=2.3.1
+asciidoctorj24Version=2.4.0
 org.gradle.daemon=false

spring-restdocs-asciidoctor/build.gradle

@@ -28,6 +28,12 @@ matrixTest {
 	asciidoctorj {
 		group = 'org.asciidoctor'
 		artifact = 'asciidoctorj'
-		versions = [ asciidoctorj16Version, asciidoctorj20Version, asciidoctorj21Version ]
+		versions = [ asciidoctorj16Version,
+			asciidoctorj20Version,
+			asciidoctorj21Version,
+			asciidoctorj22Version,
+			asciidoctorj23Version,
+			asciidoctorj24Version
+		]
 	}
 }