about widget: Center multi-line social icons

Center social icons when there is more than one line.

See #494

layouts/partials/css/academic.css

@@ -469,6 +469,7 @@ a[data-fancybox] img {
   display: inline-flex;
   flex-direction: row;
   flex-wrap: wrap;
+  justify-content: center;
   list-style: none;
   padding: 0;
   margin-top: 30px;