update HISTORY.md and version.h for 6.11.4

HISTORY.md

 # Rocksdb Change Log
-## Unreleased
+## 6.11.4 (7/15/2020)
 ### Bug Fixes
 * Make compaction report InternalKey corruption while iterating over the input.
 

include/rocksdb/version.h

@@ -6,7 +6,7 @@
 
 #define ROCKSDB_MAJOR 6
 #define ROCKSDB_MINOR 11
-#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