Require punycode with trailing slash

[imcotton]

Quote from Punycode.js README:

⚠️ Note that userland modules don't hide core modules. For example, require('punycode') still imports the deprecated core module even if you executed npm install punycode. Use require('punycode/') to import userland modules rather than core modules.

[domenic]

I believe this note is no longer true, as you can test by uninstalling punycode and then the tests will fail.

[imcotton]

By run:

NODE_PENDING_DEPRECATION=1 npm test | grep DEP

Gives:

[DEP0040] DeprecationWarning: The punycode module is deprecated. Please use a userland alternative instead.

In Node.js v16

[imcotton]

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