[Build] Updating lombok plugin (#50)

This fixes build issues when using JDK 16.

Author: sh54

imgui-app/build.gradle

@@ -1,6 +1,6 @@
 plugins {
     id 'java-library'
-    id 'io.freefair.lombok' version '5.3.0'
+    id 'io.freefair.lombok' version '6.0.0-m2'
     id 'checkstyle'
     id 'maven-publish'
     id 'signing'