Regression 13.5.1: isURL() fails for number urls, e.g. 1234.com

[mbalaam]

Describe the bug
Using 13.1.17 we have a test for the url http://1337.net (yes, very much lols) which passed, and as far as I can see appears to be a valid url.

This is now failing on 13.5.1, if I try changing to http://l337.net or http://133t.net then the tests pass.

Additional context
Validator.js version: 13.5.1
Node.js version: v12.18.2
OS platform: macOS

[profnandaa]

Fixed in #1546 -- will release this patch as a hotfix due to the regression.