Examples update - use behind proxy

[jbbeauf]

Hello,

New example proposal: behind a proxy, useful for corporate usage

// With ES5
var JiraApi = require('jira-client');
var rp = require('request-promise');

// Initialize
var jira = new JiraApi({
  protocol: 'https',
  host: 'jira.somehost.com',
  username: 'username',
  password: 'password',
  apiVersion: '2',
  strictSSL: true,
  promise = rp.defaults({
    "proxy": "http:/proxyUsername:proxyPasswor@10.11.12.13:8080" // note for proxyPasswor: replace all special characters with unicode hexs
  })
});

....

Thanks !