Results 3 issues of kebyn

When I use `ldap` authentication in `vsftpd`, I found `nss-pam-ldapd` and `linux-pam` installation package, no `pam_ldap.conf` file configuration, and `pam authentication` can not be used, I have been tested on...

question

1. Use `go mod` to manage dependencies 2. Update the `Dockerfile`, the generated images are smaller

1. Fix code formatting according to go-staticcheck 2. Some known issues have been fixed