Update spring-asciidoctor-backends to 0.0.5

Closes gh-1192

Author: jgrandja

buildSrc/src/main/java/org/springframework/gradle/docs/SpringAsciidoctorPlugin.java

@@ -104,7 +104,7 @@ private void createAsciidoctorExtensionsConfiguration(Project project) {
 			project.getConfigurations().matching((candidate) -> "management".equals(candidate.getName()))
 					.all(configuration::extendsFrom);
 			configuration.getDependencies().add(project.getDependencies()
-					.create("io.spring.asciidoctor.backends:spring-asciidoctor-backends:0.0.3"));
+					.create("io.spring.asciidoctor.backends:spring-asciidoctor-backends:0.0.5"));
 			configuration.getDependencies()
 					.add(project.getDependencies().create("org.asciidoctor:asciidoctorj-pdf:1.5.3"));
 		});