Class TableHeader to_html method does not use correct table tags

[Cerebex]

The current code is as follows:

def to_html(self, include_children=False, recurse=False):
    """
    Returns html for a <th> with html from all the cells in the row as <td>
    """
    html_str = "<th>"
    for cell in self.cells:
        html_str = html_str + cell.to_html()
    html_str = html_str + "</th>"
    return html_str

The proper format for html tables is shown here: w3 school html tables

<table>
  <tr>
    <th>Company</th>
    <th>Contact</th>
    <th>Country</th>
  </tr>
  <tr>
    <td>Alfreds Futterkiste</td>
    <td>Maria Anders</td>
    <td>Germany</td>
  </tr>
  <tr>
    <td>Centro comercial Moctezuma</td>
    <td>Francisco Chang</td>
    <td>Mexico</td>
  </tr>
</table>

For this reason, this function should instead returns html for a with html from all the cells in the row as .

This means this to_html must be changed from to and the class TableCell to_html method most likely needs to be changed aswell to make sure for header rows the encompassing tags are instead of .