Upgrade to Asciidoctor PDF 2.3.0

Closes gh-858

Author: wilkinsona

spring-restdocs-platform/build.gradle

@@ -14,7 +14,7 @@ dependencies {
 		api("junit:junit:4.12")
 		api("org.apache.pdfbox:pdfbox:2.0.27")
 		api("org.asciidoctor:asciidoctorj:2.5.6")
-		api("org.asciidoctor:asciidoctorj-pdf:2.1.4")
+		api("org.asciidoctor:asciidoctorj-pdf:2.3.0")
 		api("org.assertj:assertj-core:3.23.1")
 		api("org.hamcrest:hamcrest-core:1.3")
 		api("org.hamcrest:hamcrest-library:1.3")