Fix javaDoc publishing.

Author: SimY4

build.gradle

@@ -38,6 +38,21 @@ subprojects {
     test {
         useJUnitPlatform()
     }
+
+    javadoc {
+        source = sourceSets.main.allJava
+        classpath = configurations.compileClasspath
+
+        options {
+            setMemberLevel JavadocMemberLevel.PUBLIC
+            setAuthor true
+
+            links "https://docs.oracle.com/javase/6/docs/api/"
+        }
+        if(JavaVersion.current().isJava9Compatible()) {
+            options.addBooleanOption('html4', true)
+        }
+    }
 }
 
 task wrapper(type: Wrapper) {

gradle/check-errorprone.gradle

@@ -1,6 +1,6 @@
 import org.gradle.internal.jvm.Jvm
 
-if (!Jvm.current().javaVersion.java9Compatible) {
+if (!JavaVersion.current().isJava9Compatible()) {
     apply plugin: 'net.ltgt.errorprone'
 
     dependencies {

gradle/publish-maven.gradle

@@ -8,7 +8,7 @@ task sourcesJar(type: Jar) {
 
 task javadocJar(type: Jar) {
     classifier 'javadoc'
-    from javadoc.destinationDir
+    from javadoc
 }
 
 publishing {