Describe the bug
Although trying to be generic for different protocols the isURL check always valdiates hosts even if no host specified.

Examples
My use case is to validate a postgresql uri with using a unix socket which could look like:

postgres://user:pw@/test?host=/var/run/postgresql

isURL always returns false, not matter which options specified, even with require_host=false.

if i change the url to:

postgres://user:pw@localhost.com/test?host=/var/run/postgresql

it would validate to true.

Additional context
Validator.js version: 13.7.0 (current HEAD)
Node.js version: doesn't matter
OS platform: doesn't matter