查找服务器
用法：
$ find-server localhost 8080
8088
$ find-server localhost 8080 8085
Could not find server
$ echo $?
1
$ find-server localhost 5000
Could not find server
$ echo $?
1
var findServer = require ( 'find-server' ) ;
findServer ( 'localhost' , 8000 , 9000 , function ( err , port ) {
console . log ( port ) ;
} ) ;
