update 5.5 change log

Summary:
update bug fixed.
Closes https://github.com/facebook/rocksdb/pull/2434

Differential Revision: D5218601

Pulled By: lightmark

fbshipit-source-id: 1f86b2c93345673612381081537d464e7d12e434

HISTORY.md

@@ -24,7 +24,10 @@
 * Add debugging function `GetAllKeyVersions` to see internal versions of a range of keys.
 * Support file ingestion with universal compaction style
 * Support file ingestion behind with option `allow_ingest_behind`
-* New option enable_pipelined_write which may improve write throughput in case writing from multiple threads and WAL enabled .
+* New option enable_pipelined_write which may improve write throughput in case writing from multiple threads and WAL enabled.
+
+### Bug Fixes
+* Fix the bug that Direct I/O uses direct reads for non-SST file
 
 ## 5.4.0 (04/11/2017)
 ### Public API Change