Use socket.destroy() not socket.end() on successful connection

When socket.end() is called, a FIN packet is sent however if the
other host does not respond the socket will timeout and so this
module will report 'closed'. The port is open but the other host
is misbehaving.
This fix just forces the connection to be destroyed immediately and
so means that a successful connection will always result in an 'open'
status being reported.
Merge pull request #19 from thomseddon/fix-end

Use socket.destroy() not socket.end() on successful connection