Fix DeprecationWarning for newer versions of node

[dante0624]

Describe the bug
When using htmlhint, a deprecation warning appears saying:
"(node:71320) [DEP0040] DeprecationWarning: The punycode module is deprecated. Please use a userland alternative instead."

This module has been deprecated since node v7.0.0

To Reproduce
-- Simply invoke htmlhint via the CLI with a node version newer than v7.0.0

Cause of Error
I backtracked to see where this punycode module is invoked. The root cause is version locking the dependency "node-fetch" to version "2.6.2" within package.json.

This is a much older version of node-fetch, which itself has a dependency of "whatwg-url" at version "5.0.0". This is the package which finally uses the punycode module. On my machine, I simply opened the file htmlhint/node_modules/whatwg-url/lib/url-state-machine.js and saw that line 2 was "const punycode = require("punycode");"

Solution
Bumping node-fetch to a newer version will likely solve this problem. Hope this is all helpful!

Importance
Although this issue does not break htmlhint at the moment, it may break it in later versions of node