Add HTML5 option for Javadoc

Author: laurentpellegrino

build.gradle

@@ -121,6 +121,12 @@ signing {
     sign publishing.publications.mavenJava
 }
 
+javadoc {
+    if(JavaVersion.current().isJava9Compatible()) {
+        options.addBooleanOption('html5', true)
+    }
+}
+
 sourceSets {
     integrationTest {
         compileClasspath += sourceSets.main.output