title: How to make a partial record with io-ts?
body: <p>How does one make a partial record in <code>io-ts</code>?</p>
  <p>I want to achieve something similar using <code>io-ts</code> and <code>t.partial</code> does not appear to accept <code>t.record</code> as a prop.</p>
  <pre class="lang-js prettyprint-override"><code>type Pets = keyof { dog: undefined; cat: undefined; fish: undefined };
  interface PetCounts extends Partial&lt;Record&lt;Pets, number&gt;&gt; {}
  </code></pre>