fix external link icon

Author: michaelmattig

theme/index.hbs

@@ -137,7 +137,7 @@
                 <li class="chapter-item">
                     <a href="https://python.docs.geoengine.io" style="width: 100%; display: flex; flex-direction: row;">
                         <span style="flex: 1;">Python</span>
-                        <i class="fa fa-external-link" style="align-self: center;"></i>
+                        <span style="align-self: center;">{{fa "solid" "arrow-up-right-from-square"}}</span>
                     </a>
                 </li>
             </ol>