Add popover=hint in attribute summary table

Author: foolip

source

@@ -144957,6 +144957,7 @@ interface <dfn interface>External</dfn> {
      <td> Makes the element a <span data-x="attr-popover">popover</span> element
      <td> "<code data-x="attr-popover-auto">auto</code>";
           "<code data-x="attr-popover-manual">manual</code>";
+          "<code data-x="attr-popover-hint">hint</code>"
     <tr>
      <th> <code data-x="">popovertarget</code>
      <td> <code data-x="attr-popovertarget">button</code>;