Have to change the code below to enable "Subscribe" button.
<form method="post" action="/subscribe/" class="">
<input class="confirm" type="hidden" name="confirm" /><input class="location" type="hidden" name="location" /><input class="referrer" type="hidden" name="referrer" />
<div class="form-group">
<input class="subscribe-email" type="email" name="email" placeholder="[email protected]" />
</div>
<button class="" type="submit" {% unless site.subscribe %}enabled{% endunless %}><span>Subscribe</span></button>
<script type="text/javascript">(function(g,h,o,s,t){h[o]('.location')[s]=h[o]('.location')[s] || g.location.href;h[o]('.referrer')[s]=h[o]('.referrer')[s] || h.referrer;})(window,document,'querySelector','value');</script>
</form>