Contributors table: keep every row at seven cells (#2938)

The last row carries eight <td> elements while all fifty-three others carry
seven. Each cell is fixed at width="14.28%" (one seventh), so eight of them
overflow the table: the final avatar renders narrower than the rest and sits
past the edge, reachable only by scrolling horizontally.

Moving that one cell onto its own row restores the invariant. Verified by
counting cells per row before and after: the distribution goes from {7, 8} to
{7, 1}, the 1 being the new trailing row that the next contributor fills.

README.md

@@ -547,6 +547,8 @@ Thanks goes to these wonderful people ([emoji key](./CONTRIBUTING.md#contributor
       <td align="center" valign="top" width="14.28%"><a href="https://www.cloudblogger.eu"><img src="https://avatars.githubusercontent.com/u/53148138?v=4" width="100px;" alt=""/><br /><sub><b>Konstantinos Passadis | Azure MVP | MCT</b></sub></a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/alx-so"><img src="https://avatars.githubusercontent.com/u/8975621?v=4" width="100px;" alt=""/><br /><sub><b>Alex Sokol</b></sub></a></td>
       <td align="center" valign="top" width="14.28%"><a href="http://blogs.gnome.org/jmatsuzawa/"><img src="https://avatars.githubusercontent.com/u/545426?v=4" width="100px;" alt=""/><br /><sub><b>Jiro Matsuzawa</b></sub></a></td>
+    </tr>
+    <tr>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/GuoCheng24"><img src="https://avatars.githubusercontent.com/u/224264187?v=4" width="100px;" alt=""/><br /><sub><b>Guo Cheng</b></sub></a></td>
     </tr>
   </tbody>