Update HISTORY.mc for 4.4.0

Summary: Prepare to cut release

Test Plan: no code change.

Reviewers: yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D52827

HISTORY.md

 # Rocksdb Change Log
 
-## Unreleased
+## 4.4.0 (1/14/2016)
 ### Public API Changes
 * Change names in CompactionPri and add a new one.
 * Deprecate options.soft_rate_limit and add options.soft_pending_compaction_bytes_limit.