Whether the value is hostname format or not.

import { isHostnameFormat } from "https://deno.land/x/isx@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";
assertEquals(isHostnameFormat("a"), true);
assertEquals(isHostnameFormat("test.test"), true);
assertEquals(isHostnameFormat("."), false);