Bump org.apache.zookeeper:zookeeper from 3.6.3 to 3.8.4

Bumps org.apache.zookeeper:zookeeper from 3.6.3 to 3.8.4.

---
updated-dependencies:
- dependency-name: org.apache.zookeeper:zookeeper
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index a07db0f..85bfe1e 100644
--- a/pom.xml
+++ b/pom.xml
@@ -80,7 +80,7 @@
     <flink.main.version>1.17</flink.main.version>
     <flink.version>1.17.1</flink.version>
     <flink.python.artifact>flink-python</flink.python.artifact>
-    <zookeeper.version>3.6.3</zookeeper.version>
+    <zookeeper.version>3.8.4</zookeeper.version>
     <hadoop.version>2.10.2</hadoop.version>
 
     <!-- Can be set to any value to reproduce a specific build. -->