fixed build. I'm embarassed that I didn't notice the empty JAR file.

build.gradle

@@ -1,4 +1,15 @@
+buildscript {
+    ext.kotlin_version = '1.1.60'
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
 apply plugin: 'java'
+apply plugin: 'kotlin'
 apply plugin: 'maven'
 apply plugin: 'signing'
 apply plugin: 'jacoco'
@@ -12,6 +23,9 @@ repositories {
 }
 
 dependencies {
+    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
+    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+
     testCompile group: 'junit', name: 'junit', version: '4.11'
 }