URL: add path setter tests for parent directory

[watilde]

I found out a gap between WHATWG's URL and Node.js as the below and add the test to capture it.

const NodeURL = require("url").URL;
const WhatwgURL = require("../whatwg-url/").URL;
const newPath = '/..';

const url = new NodeURL("foo://path/to");  
url.pathname = newPath;
console.log(url.href); // => foo://path

const url2 = new WhatwgURL("foo://path/to");
url2.pathname = newPath;
console.log(url2.href); // => foo://path/