Update slack link

Author: cstrap

index.html

@@ -124,7 +124,7 @@ <h3>Podcast</h3>
                     </div>
                     <div class="4u 12u(mobile)">
                         <section class="box style1">
-                            <a href="https://join.slack.com/t/pythonmilano/shared_invite/zt-1jxihttcl-WxvgkHDmd01fBhH9YugKBw">
+                            <a href="https://bit.ly/pymislack">
                                 <span class="icon featured fa-slack"></span>
                                 <h3>Slack</h3>
                                 <p>Canale di comunicazione veloce per organizzare i meetup e anche per far quattro chiacchiere.</p>