fix build failure due to indirect dependency on jcenter

(cherry picked from commit 8761fac80534a0ccf3dff208c0109161e52bacae)
diff --git a/build.gradle b/build.gradle
index 77acecf..551fdf9 100644
--- a/build.gradle
+++ b/build.gradle
@@ -16,7 +16,7 @@
  */
 
 plugins {
-    id "org.nosphere.apache.rat" version "0.3.0"
+    id "org.nosphere.apache.rat" version "0.6.0"
     id "com.diffplug.gradle.spotless" version "3.0.0"
     id "de.undercouch.download" version "3.1.2"
 }
diff --git a/gradle/rat.gradle b/gradle/rat.gradle
index 2aedfe0..b22e4fe 100644
--- a/gradle/rat.gradle
+++ b/gradle/rat.gradle
@@ -17,10 +17,6 @@
 apply plugin: "org.nosphere.apache.rat"
 
 rat {
-  xmlOutput = false
-  htmlOutput = false
-  plainOutput = true
-
   excludes = [
     // git
     '.git/**',