MINOR: Upgraded RocksDB to 5.3.6

Solves a problem as described here: https://groups.google.com/forum/#!topic/confluent-platform/cR02K2o6BIw

Author: Eno Thereska <eno.thereska@gmail.com>

Reviewers: Damian Guy <damian.guy@gmail.com>

Closes #3472 from enothereska/minor-upgrade-rocksdb-5.1.2

gradle/dependencies.gradle

@@ -62,7 +62,7 @@ versions += [
   metrics: "2.2.0",
   powermock: "1.6.4",
   reflections: "0.9.11",
-  rocksDB: "5.0.1",
+  rocksDB: "5.3.6",
   scalaTest: "3.0.2",
   scalaParserCombinators: "1.0.4",
   scoverage: "1.3.0",