Add missing include to use std::unique_ptr

This was causing issues when including this header from another file.

include/rocksdb/compaction_filter.h

@@ -9,6 +9,7 @@
 #ifndef STORAGE_ROCKSDB_INCLUDE_COMPACTION_FILTER_H_
 #define STORAGE_ROCKSDB_INCLUDE_COMPACTION_FILTER_H_
 
+#include <memory>
 #include <string>
 #include <vector>