Fix migration comment (#1241)

models/migrations/migrations.go

 	NewMigration("use new avatar path name for security reason", useNewNameAvatars),
 	// v21 -> v22
 	NewMigration("rewrite authorized_keys file via new format", useNewPublickeyFormat),
-	// v21 -> v22
+	// v22 -> v23
 	NewMigration("generate and migrate wiki Git hooks", generateAndMigrateWikiGitHooks),
 }