Update sidebar.less

Fixes https://github.com/almasaeed2010/AdminLTE/issues/1158: expandable indicators of sidebar's expandable menu items didn't toggle (rotate) upon expansion.

build/less/sidebar.less

@@ -121,7 +121,7 @@
     margin-right: 10px;
   }
   li.active {
-    > a > .fa-angle-left
+    > a > .fa-angle-left,
     > a > .pull-right-container > .fa-angle-left {
       .rotate(-90deg);
     }