docs: fix slack invite (#260)

Closes #259

Signed-off-by: Gabriele Bartolini <[email protected]>

Author: gbartolini

layouts/partials/nav.html

@@ -58,7 +58,7 @@
         <a class="github-button" href="https://github.com/cloudnative-pg/cloudnative-pg"
           data-color-scheme="no-preference: light; light: light; dark: dark;" data-size="large" data-show-count="true"
           aria-label="Star cloudnative-pg/cloudnative-pg on GitHub">Star</a>
-        <a href="https://join.slack.com/t/cloudnativepg/shared_invite/zt-237bhehx3-htDW2kz2hKJxEhn1W4VTnw">
+        <a href="https://join.slack.com/t/cloudnativepg/shared_invite/zt-30a6l6bp3-u1lNAmh~N02Cfiv2utKTFg">
           <img src="/icons/Slack.svg" alt="Slack" title="Join our Slack channel now!">
         </a>
         <a href="https://twitter.com/CloudNativePg">
@@ -78,4 +78,4 @@
   toggleButton.addEventListener('click', () => {
     naviList.classList.toggle('hidden');
   })
-</script>
+</script>