title: Make Woocommerce checkout state field required
body: <p>So this problem may have a easy solution, but I'm stuck for the moment. After the last update (Woocommerce 3.3.5) I have a problem with the state field on the checkout page, because it is not mandatory and people just skip it. I really need this thing to be mandatory, because I have connected my website to the delivery company server through and API to send the order info directly to them. </p>
  
  <p>I tried adding this to my functions.php and the thing is that when I go to the checkout page, the field has an asterisk, but for like one second.</p>
  
  <pre><code>add_filter( 'woocommerce_billing_fields', 'woo_filter_state_billing', 
  10, 1 );
  add_filter( 'woocommerce_shipping_fields', 
  'woo_filter_state_shipping', 10, 1 );
  
  function woo_filter_state_billing( $address_fields ) { 
  $address_fields['billing_state']['required'] = true;
  return $address_fields;
  }
  function woo_filter_state_shipping( $address_fields ) { 
  $address_fields['shipping_state']['required'] = true;
  return $address_fields;
  }
  </code></pre>
  
  <p>Any help is appreciated. Thanks!</p>