explorer/python: Fix typo in table template

bin/explorer/python/templates/index.html

@@ -100,7 +100,7 @@
               <td>{{ block.size }}</td>
               <td>{{ block.n_txs }}</td>
               <td>{{ block.timestamp }}</td>
-              <th>{{ block.powtype }}</td>
+              <td>{{ block.powtype }}</td>
               <td><a href="/block/{{ block.height }}">{{ block.hash }}</a></td>
             </tr>
             {% endfor %}