Fix typo (#7353)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/7353

Reviewed By: ajkr

Differential Revision: D23585525

Pulled By: zhichao-cao

fbshipit-source-id: 3f72d9663ec207b9dfe6b287d455a13d3c86879f

table/plain/plain_table_index.h

@@ -20,7 +20,7 @@ namespace ROCKSDB_NAMESPACE {
 
 // The file contains two classes PlainTableIndex and PlainTableIndexBuilder
 // The two classes implement the index format of PlainTable.
-// For descripton of PlainTable format, see comments of class
+// For description of PlainTable format, see comments of class
 // PlainTableFactory
 //
 //