Update tuf-spec.md

Co-Authored-By: lukpueh <[email protected]>

Author: mnm678

tuf-spec.md

@@ -1134,7 +1134,7 @@ repo](https://github.com/theupdateframework/specification/issues).
     metadata files.
 
     * **1.9.3**. **Timestamp recovery** If a threshold of timestamp keys are
-    removed from the root metadata, delete the old timestamp metadata files.
+    removed from the root metadata, delete the old timestamp metadata file.
 
   * **1.10**. **Set whether consistent snapshots are used as per the trusted
   root metadata file** (see Section 4.3).