refresh captcha if it is wrong

static/main.js

@@ -16,6 +16,8 @@ async function formClick(ev) {
 
     let json = await fetched.json();
 
+    target.querySelector('.captcha').src += '&a=b';
+
     target.querySelector('.form-message').textContent = json.message;
 
     if (json.redirect) {

views/form_bare.ejs

@@ -5,7 +5,7 @@
     <div class='form-message'></div>
     <% if (!noCaptcha) { %>
         <span class='form-key'>
-            <img class='captcha' src='/client/captcha'>
+            <img class='captcha' src='/client/captcha?a'>
         </span>
         <input class='form-input' type='text' name='challenger' value='Type the captcha'>
         <% } %>