update to gradle 6.9, jdk 15, update findbugs
diff --git a/lib/java/build.gradle b/lib/java/build.gradle
index e88ff12..ad30249 100644
--- a/lib/java/build.gradle
+++ b/lib/java/build.gradle
@@ -40,12 +40,7 @@
     id 'maven'
     id 'signing'
     id 'com.github.johnrengelman.shadow' version '4.0.4'
-    id "com.github.spotbugs" version "2.0.0"
-}
-
-ext {
-    // https://github.com/spotbugs/spotbugs-gradle-plugin/issues/32#issuecomment-409951172
-    SpotBugsTask = com.github.spotbugs.SpotBugsTask
+    id "com.github.spotbugs" version "4.7.1"
 }
 
 description = 'Apache Thrift Java Library'