Abort TCP connection request on .end()

[Aareksio]

Test:

const Steam = require('./');

const httpProxy = 'http://98.76.54.32';

const client = new Steam.CMClient();

client.on('debug', (...data) => console.log(...data));

client.setHttpProxy(httpProxy);

client.connect();
client.connect();

Before:

TypeError: self._connection.setTimeout is not a function
    at node-steam-client\lib\cm_client.js:175:21

After:

No error

Fixes #14