build:javadoc: use JavaVersion.current().isJava8Compatible()

common.gradle

@@ -37,7 +37,7 @@ javadoc {
     options.author = "true"
     options.use = "true"
     //disable doclint for JDK8, more quiet output
-    if (Double.parseDouble(System.getProperty("java.specification.version")) > 1.7){
+    if (JavaVersion.current().isJava8Compatible()){
         options.addStringOption('Xdoclint:none', '-quiet')
     }
 }