closest() should be able to start from text nodes

[Qualtagh]

A function closest() is now working only on tags. It used to work on text nodes too on 1.0.0-rc.10.

Breaking commit: #2057

parent(), parents() and parentsUntil() functions still work for text nodes though. I expect closest() to behave the same way.

Example:

const cheerio = require('cheerio');
const $ = cheerio.load('<span>abc</span>');
const textNode = $('span').contents().first();
console.log(textNode.closest('span').length);

Expected output is 1 (i.e. closest span has been found), current version returns 0.

I'll create a pull request soon.