fix: expose errors as export

ftp-srv.js

@@ -1,6 +1,8 @@
 const FtpSrv = require('./src');
 const FileSystem = require('./src/fs');
+const errors = require('./src/errors');
 
 module.exports = FtpSrv;
 module.exports.FtpSrv = FtpSrv;
 module.exports.FileSystem = FileSystem;
+module.exports.ftpErrors = errors;