Removed gradient from attribute table headers in IE

Author: emzeq

lib/active_admin/stylesheets/active_admin.scss

@@ -359,6 +359,10 @@ table.dashboard {
   th {
     @include no-shadow;
     background: none;
+    // IE 6 & 7
+    filter: progid:DXImageTransform.Microsoft.gradient(enabled = false);
+    // IE 8
+    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(enabled=false)";
     width: 150px;
     font-size: 0.9em;
     padding-left: 0;