bump version to 5.12.4 and update history

HISTORY.md

@@ -2,6 +2,7 @@
 ## 5.12.3 (04/09/2018)
 ### Bug Fixes
 * Fix memory leak when pin_l0_filter_and_index_blocks_in_cache is used with partitioned filters
+* Fix memory leak in two_level_iterator
 
 ## 5.12.2 (3/23/2018)
 ### Bug Fixes

include/rocksdb/version.h

@@ -6,7 +6,7 @@
 
 #define ROCKSDB_MAJOR 5
 #define ROCKSDB_MINOR 12
-#define ROCKSDB_PATCH 3
+#define ROCKSDB_PATCH 4
 
 // Do not use these. We made the mistake of declaring macros starting with
 // double underscore. Now we have to live with our choice. We'll deprecate these