reset grecaptcha in case of error

public/static/js/mapguesser.js

@@ -89,6 +89,9 @@ var MapGuesser = {
 
                     formError.style.display = 'block';
                     formError.innerHTML = this.response.error.errorText;
+                    if (typeof grecaptcha !== 'undefined') {
+                        grecaptcha.reset();
+                    }
 
                     return;
                 }