Update HISTORY and version.h for 6.27 release (#9192)

Summary:
As title.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9192

Reviewed By: ltamasi

Differential Revision: D32578141

Pulled By: riversand963

fbshipit-source-id: 16216451c87e383ca8fd309acf15106e46172aaa

HISTORY.md

@@ -1,5 +1,5 @@
 # Rocksdb Change Log
-## Unreleased
+## 6.27.0 (2021-11-19)
 ### New Features
 * Added new ChecksumType kXXH3 which is faster than kCRC32c on almost all x86\_64 hardware.
 * Added a new online consistency check for BlobDB which validates that the number/total size of garbage blobs does not exceed the number/total size of all blobs in any given blob file.

include/rocksdb/version.h

@@ -10,7 +10,7 @@
 #include "rocksdb/rocksdb_namespace.h"
 
 #define ROCKSDB_MAJOR 6
-#define ROCKSDB_MINOR 26
+#define ROCKSDB_MINOR 27
 #define ROCKSDB_PATCH 0
 
 // Do not use these. We made the mistake of declaring macros starting with