fix: use font-awesome for icons

update "group" icon

Author: maxceem

src/components/challenge-users-stats/challenge-users-stats.directive.html

@@ -1,14 +1,14 @@
 <div class="challenge-users-stats">
   <span class="challenge-users-stats-type" title="{{registrants}} registrants" alt="{{registrants}} registrants">
-    <i class="glyphicon glyphicon-user"></i>
+    <i class="fa fa-user"></i>
     <span>{{registrants}}</span>
   </span>
   <span class="challenge-users-stats-type" title="{{submissions}} submissions" alt="{{submissions}} submissions">
-    <i class="glyphicon glyphicon-file"></i>
+    <i class="fa fa-file"></i>
     <span>{{submissions}}</span>
   </span>
   <span class="challenge-users-stats-type" title="{{groups}} groups" alt="{{groups}} groups">
-    <i class="glyphicon glyphicon-tower"></i>
+    <i class="fa fa-group"></i>
     <span>{{groups}}</span>
   </span>
 </div>