Update rocksdb to v5.17.2

CHANGELOG.md

 # Changelog
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+- Updated rocksdb to v5.17.2
+
 ## 0.3.4 (2018-10-09)
 - Updated rocksdb dependency to v5.15.10.
 - Added `TYPE` command.

rocksdb @ f438b98e

-Subproject commit 7e1f37eb4fc711dbf3ecc9610178931f00754de8
+Subproject commit f438b98e552010613cff8684a7d84191ed785148