update HISTORY with recent changes

Summary:
We should mention these:

- `EventListener::OnStallConditionsChanged()` in 01542400a8
- `DeleteRange()` fix in 966b32b57c
Closes https://github.com/facebook/rocksdb/pull/3054

Differential Revision: D6113989

Pulled By: ajkr

fbshipit-source-id: d5e058e1ab07570df22936e8d5939fb30fb4d381

HISTORY.md

@@ -7,9 +7,11 @@
 * `DBOptions::bytes_per_sync` and `DBOptions::wal_bytes_per_sync` can now be changed dynamically, `DBOptions::wal_bytes_per_sync` will flush all memtables and switch to a new WAL file.
 * Support dynamic adjustment of rate limit according to demand for background I/O. It can be enabled by passing `true` to the `auto_tuned` parameter in `NewGenericRateLimiter()`. The value passed as `rate_bytes_per_sec` will still be respected as an upper-bound.
 * Support dynamically changing `ColumnFamilyOptions::compaction_options_fifo`.
+* Introduce `EventListener::OnStallConditionsChanged()` callback. Users can implement it to be notified when user writes are stalled, stopped, or resumed.
 
 ### Bug Fixes
 * Fix a potential data inconsistency issue during point-in-time recovery. `DB:Open()` will abort if column family inconsistency is found during PIT recovery.
+* Fix possible metadata corruption in databases using `DeleteRange()`.
 
 ## 5.8.0 (08/30/2017)
 ### Public API Change