Minor typo in comment (s/pro/pri)

Summary: Closes https://github.com/facebook/rocksdb/pull/3460

Differential Revision: D6895365

Pulled By: miasantreble

fbshipit-source-id: 04f633d1971b1f542ac28118b738ceb0242a0228

cache/lru_cache.h

@@ -57,7 +57,7 @@ struct LRUHandle {
   // Include the following flags:
   //   in_cache:    whether this entry is referenced by the hash table.
   //   is_high_pri: whether this entry is high priority entry.
-  //   in_high_pro_pool: whether this entry is in high-pri pool.
+  //   in_high_pri_pool: whether this entry is in high-pri pool.
   char flags;
 
   uint32_t hash;     // Hash of key(); used for fast sharding and comparisons