Ruby-expect script example?

since openwrt package has only ruby-expect for expect function,
i'm trying to use script for ssh to host
i found this example in link below

however when i use that script, it gives me error
"`require': cannot load such file -- ruby_expect (LoadError)"
anybody can help how to use ruby-expect?

I make simple script below

#!/overlay/upper/usr/bin/ruby --verbose

require 'expect'

username = 'admin'
password = 'xxx'
hostname = ''

spawn("/usr/bin/ssh #{username}@#{hostname}") do
  expect(/password: /) do
    send password

terminal show

~# admin@'s password:

/usr/bin/ssh: Connection to admin@ exited: Interrupted.

login still unsuccessfull
confused how???