Upgrade to org.asciidoctor.convert 1.5.6

Closes gh-459

docs/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id 'org.asciidoctor.convert' version '1.5.3'
+	id 'org.asciidoctor.convert' version '1.5.6'
 }
 
 repositories {
@@ -28,4 +28,4 @@ asciidoctor {
 	attributes	'revnumber': project.version,
 				'branch-or-tag': project.version.endsWith('SNAPSHOT') ? 'master': "v${project.version}"
 	inputs.files(sourceSets.test.java)
-}
+}

docs/src/docs/asciidoc/getting-started.adoc

@@ -154,7 +154,7 @@ the configuration are described below.
 .Gradle
 ----
 	plugins { <1>
-		id "org.asciidoctor.convert" version "1.5.3"
+		id "org.asciidoctor.convert" version "1.5.6"
 	}
 
 	dependencies {

samples/junit5/build.gradle

@@ -9,7 +9,7 @@ buildscript {
 }
 
 plugins {
-	id "org.asciidoctor.convert" version "1.5.3"
+	id "org.asciidoctor.convert" version "1.5.6"
 }
 
 apply plugin: 'java'

samples/rest-assured/build.gradle

@@ -8,7 +8,7 @@ buildscript {
 }
 
 plugins {
-	id "org.asciidoctor.convert" version "1.5.3"
+	id "org.asciidoctor.convert" version "1.5.6"
 }
 
 apply plugin: 'java'

samples/rest-notes-grails/build.gradle

@@ -9,7 +9,7 @@ buildscript {
 }
 
 plugins {
-	id 'org.asciidoctor.convert' version '1.5.3'
+	id 'org.asciidoctor.convert' version '1.5.6'
 }
 
 version "0.1"

samples/rest-notes-spring-hateoas/build.gradle

@@ -8,7 +8,7 @@ buildscript {
 }
 
 plugins {
-	id "org.asciidoctor.convert" version "1.5.3"
+	id "org.asciidoctor.convert" version "1.5.6"
 }
 
 apply plugin: 'java'

samples/testng/build.gradle

@@ -8,7 +8,7 @@ buildscript {
 }
 
 plugins {
-	id "org.asciidoctor.convert" version "1.5.3"
+	id "org.asciidoctor.convert" version "1.5.6"
 }
 
 apply plugin: 'java'

samples/web-test-client/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.asciidoctor.convert" version "1.5.3"
+	id "org.asciidoctor.convert" version "1.5.6"
 }
 
 apply plugin: 'java'