fix altcha url

use `site.Params` to access site params, see https://gohugo.io/functions/global/site/

Author: overheadhunter

layouts/partials/captcha.html

@@ -1,5 +1,5 @@
 <altcha-widget
-  challengeurl="{{ .Site.Params.baseApiUrl }}/altcha/challenge.php"
+  challengeurl="{{ site.Params.baseApiUrl }}/altcha/challenge.php"
   hidelogo
   hidefooter
   floating="auto"