fix: slack link

Author: moshfeu

content/email_templates/layout.html

@@ -461,7 +461,7 @@
                                       <td style="
 padding: 0 5px;
 ">
-                                        <a href="https://join.slack.com/t/coding-coach/shared_invite/enQtODYwODU0NDE2OTkzLTRmMTY3NTZmOGI2MjYyZTM2ZDBlZTNjNmMwNGRhY2I3MzZkMjA3ZjlhZjliYmQzMGQyYTkxNTViZTc3MzJmOTU" title="Slack" target="_blank">
+                                        <a href="https://join.slack.com/t/coding-coach/shared_invite/zt-15kky1m4x-JrrLzQevCLkdyZiaqT_DTg" title="Slack" target="_blank">
                                           <img src="http://cdn.mcauto-images-production.sendgrid.net/83a8af126d5ca8ff/80d2f589-02ad-492e-8c97-1c712f2c0057/32x32.png" alt="LinkedIn" title="LinkedIn" width="32" style="
                                             outline: none;
                                             text-decoration: none;

content/email_templates/mentor-application-approved.html

@@ -68,7 +68,7 @@
               Join our
               <a
                 target="_blank"
-                href="https://join.slack.com/t/coding-coach/shared_invite/enQtODYwODU0NDE2OTkzLTRmMTY3NTZmOGI2MjYyZTM2ZDBlZTNjNmMwNGRhY2I3MzZkMjA3ZjlhZjliYmQzMGQyYTkxNTViZTc3MzJmOTU"
+                href="https://join.slack.com/t/coding-coach/shared_invite/zt-15kky1m4x-JrrLzQevCLkdyZiaqT_DTg"
                 >Slack</a
               >
               so you can chat real-time with other mentors and your mentees

content/email_templates/welcome.html

@@ -249,7 +249,7 @@
                           <span style="
                               font-size: 18px;
                               line-height: 25.2px;
-                            "><a href="https://join.slack.com/t/coding-coach/shared_invite/enQtODYwODU0NDE2OTkzLTRmMTY3NTZmOGI2MjYyZTM2ZDBlZTNjNmMwNGRhY2I3MzZkMjA3ZjlhZjliYmQzMGQyYTkxNTViZTc3MzJmOTU" target="_blank" rel="noopener">Join our Slack organization</a></span>
+                            "><a href="https://join.slack.com/t/coding-coach/shared_invite/zt-15kky1m4x-JrrLzQevCLkdyZiaqT_DTg" target="_blank" rel="noopener">Join our Slack organization</a></span>
                         </li>
                         <li>
                           <span style="