fix broken internal URLs in 2018/index.html and 2020/index.html

2018/index.html

@@ -170,7 +170,7 @@ of the <a href="poikola/index.html">“Most stellar” (poikola)</a>.</p>
 <p>The <a href="endoh2/index.html">“Best use of python” (endoh2)</a> is a not what you might think it is.
 It is something completely different.</p>
 <p>The <a href="ciura/index.html">“Most likely to be awarded” (ciura)</a> has an amazing vocabulary!</p>
-<p>There are also nods to entries of the years <a href="2000/bellard/index.htmk">2000/bellard</a>,
+<p>There are also nods to entries of the years <a href="2000/bellard/index.html">2000/bellard</a>,
 <a href="1989/yang/index.html">1989/yang</a>, …</p>
 <p>…We’ll stop spouting spoilers now. Have fun exploring all the entries!</p>
 <h2 id="remarks-on-some-of-submissions-that-did-not-win">Remarks on some of submissions that did not win</h2>