implement Java plugin

Author: thomasnield

build.gradle

@@ -9,11 +9,13 @@ buildscript {
 
 group = 'io.reactivex.rxjava2'
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
 
 apply plugin: 'nebula.rxjava-project'
 apply plugin: 'kotlin'
+apply plugin: 'java'
+
+sourceCompatibility = JavaVersion.VERSION_1_8
+targetCompatibility = JavaVersion.VERSION_1_8
 
 dependencies {
     compile 'io.reactivex.rxjava2:rxjava:2.0.7'