title: KnockoutValidation and the conditional required rule
body: <p>I am trying to use <a href="https://github.com/ericmbarnard/Knockout-Validation" rel="noreferrer">KnockoutValidation</a> with conditional statements. See code below:</p>
  
  <pre><code>self.transactionType = ko.observable('Option1');
  
  self.ConditionalField = ko.observable().extend({
    required: true, 
    onlyIf: self.transactionType = ="Option2"
  });
  </code></pre>
  
  <p>Unfortunately this doesn't work. I want to have <code>ConditionalField</code> only required if <code>transactionType</code> has value <code>'Option2'</code>. </p>
  
  <p>What is the best way to use conditional validation with knockout.validation.js?</p>