fails:Net::FTP#pwd sends the PWD command to the server
fails:Net::FTP#pwd returns the current directory
fails:Net::FTP#pwd raises a Net::FTPPermError when the response code is 500
fails:Net::FTP#pwd raises a Net::FTPPermError when the response code is 501
fails:Net::FTP#pwd raises a Net::FTPPermError when the response code is 502
fails:Net::FTP#pwd raises a Net::FTPTempError when the response code is 421
fails:Net::FTP#pwd raises a Net::FTPPermError when the response code is 550
