title: fastest-validator: validate two field to not be equal
body: <p>I use <a href="https://github.com/icebob/fastest-validator#equal" rel="nofollow noreferrer">fastest-validator</a> to validate an object like this:</p>
  <pre class="lang-js prettyprint-override"><code>{
      &quot;_id&quot;:&quot;619e00c177f6ea2eccffd09f&quot;,
      &quot;parent_id&quot;: &quot;619e00c177f6ea2eccffd09f&quot;,
  }
  </code></pre>
  <p><code>_id</code> and <code>parent_id</code> must not be equal. How to check that?
  I know <code>fastest-validator</code> has following validation for <a href="https://github.com/icebob/fastest-validator#equal" rel="nofollow noreferrer">equality</a>. but I need to check the opposite.
  (example for <code>type= &quot;equal&quot;</code>):</p>
  <pre class="lang-js prettyprint-override"><code>const schema = {
      password: { type: &quot;string&quot;, min: 6 },
      confirmPassword: { type: &quot;equal&quot;, field: &quot;password&quot; }
  }
  const check = v.compile(schema);
  
  check({ password: &quot;123456&quot;, confirmPassword: &quot;123456&quot; }); // Valid
  check({ password: &quot;123456&quot;, confirmPassword: &quot;pass1234&quot; }); // Fail
  
  </code></pre>
  <p>Thanks in advance</p>