fix incorrect argument passed in neighbours.encode

[uneco]

test code:

let data = {
  peers: [
    {
      id: Buffer.from('1111'),
      endpoint: {
        address: '192.168.0.1',
        udpPort: 8080,
        tcpPort: 8080,
      },
    },
    {
      id: Buffer.from('1112'),
      endpoint: {
        address: '192.168.0.2',
        udpPort: 8080,
        tcpPort: 8080,
      },
    },
  ],
  timestamp: Math.floor(new Date().getTime() / 1000),
}

console.log(hex(neighbours.encode(data)))
console.log(neighbours.decode(neighbours.encode(data)))

before this change:

Error: Invalid address: undefined
    at Object.encode (/private/tmp/test/dpt/message.js:26:11)
    at Object.encode (/private/tmp/test/dpt/message.js:56:15)
    at obj.peers.map (/private/tmp/test/dpt/message.js:124:40)
    at Array.map (<anonymous>)
    at Object.encode (/private/tmp/test/dpt/message.js:124:17)
    at Object.<anonymous> (/private/tmp/test/dpt/message.js:168:28)
    at Module._compile (module.js:641:30)
    at Object.Module._extensions..js (module.js:652:10)
    at Module.load (module.js:560:32)
    at tryModuleLoad (module.js:503:12)

after this change:

[ [ [ 'c0a80001', '1f90', '1f90', '31313131' ],
    [ 'c0a80002', '1f90', '1f90', '31313132' ] ],
  '5aaeaa28' ]
{ peers:
   [ { endpoint: [Object], id: <Buffer 31 31 31 31> },
     { endpoint: [Object], id: <Buffer 31 31 31 32> } ],
  timestamp: 1521396264 }

[uneco]

sorry, I understood that the format of decode and encode are different.