fix(toc): Use data attributes for toc

Partially fixes: #401

Signed-off-by: Khusika Dhamar Gusti <mail@khusika.com>

assets/css/_partial/_single/_toc.scss

@@ -116,7 +116,7 @@
   display: none;
   margin: .8rem 0;
 
-  &[kept=true] {
+  &[data-kept=true] {
     display: block;
   }