Fixing issue with missing remote address on slave connection.

This PR fixes the [following bug](https://travis-ci.org/attester/attester/builds/38141780#L958) randomly happening on travis after switching to Socket.io 1.1.0 and Node.js 0.10:

```
Error: getHostByAddr ENOTIMP
at errnoException (dns.js:37:11)
at Object.query [as reverse] (dns.js:156:13)
at new Slave (/home/travis/build/attester/attester/lib/test-server/slave-server.js:112:9)
at Socket.<anonymous> (/home/travis/build/attester/attester/lib/test-server/test-server.js:44:28)
at Socket.g (events.js:180:16)
at Socket.emit (events.js:95:17)
at Socket.onevent (/home/travis/build/attester/attester/node_modules/socket.io/lib/socket.js:327:8)
at Socket.onpacket (/home/travis/build/attester/attester/node_modules/socket.io/lib/socket.js:287:12)
at Client.ondecoded (/home/travis/build/attester/attester/node_modules/socket.io/lib/client.js:185:14)
at Decoder.Emitter.emit (/home/travis/build/attester/attester/node_modules/socket.io/node_modules/socket.io-parser/node_modules/component-emitter/index.js:134:20)
```

The solution is coming from https://github.com/Automattic/engine.io/commit/15afd3e2c38ee03010d98852a570849e3a9deec2