Update Gradle Asciidoctor Plugin to 4.0.0-alpha.1 (#693)

Author: puneetbehl

build.gradle

@@ -9,7 +9,7 @@ buildscript {
  classpath "io.github.groovylang.groovydoc:groovydoc-gradle-plugin:1.0.1"
  classpath "org.grails:grails-gradle-plugin:$grailsGradlePluginVersion"
  classpath "org.grails.plugins:views-gradle:2.3.2"
- classpath 'org.asciidoctor:asciidoctor-gradle-plugin:1.6.1'
+ classpath("org.asciidoctor:asciidoctor-gradle-jvm:4.0.0-alpha.1")
  classpath "com.github.erdi:webdriver-binaries-gradle-plugin:3.0"
  classpath "org.gradle:test-retry-gradle-plugin:1.5.2"
  }

docs/build.gradle

@@ -14,8 +14,8 @@ ext {
 
 version rootProject.version
 
-apply plugin: 'org.asciidoctor.convert'
 apply plugin: 'groovy'
+apply plugin: 'org.asciidoctor.jvm.convert'
 
 configurations.all {
  resolutionStrategy.eachDependency { DependencyResolveDetails details ->
@@ -66,10 +66,6 @@ asciidoctor {
  'sourcedir' : "${project.projectDir}/src/main/groovy"
 }
 
-asciidoctorj {
- version = '1.5.4'
-}
-
 task fetchSource {
  outputs.dir layout.buildDirectory.dir('checkout')
  inputs.properties(branch: githubBranch)