fix invalid markdown code blocks

For `1984/anonymous/README.md` and `2018/burton2/README.md`
a missing backquote for a markdown code block was added.

Run `make www` to perform the above.

1984/anonymous/index.html

@@ -189,13 +189,9 @@ wished to remain anonymous and they said:</p>
 <h3 id="on-the-famous-tattoo-see-above">On the famous tattoo (see above):</h3>
 <p>The author, when told about this tattoo, said:</p>
 <pre><code>    I feel honored that my entry will be the first IOCCC winning entry to become a
-    tattoo. It is the first entry to become a tattoo isn&#39;t it?
-``
-
-Landon Curt Noll, the one who told the author about the tattoo, wrote back:
-</code></pre>
-<p>Yes, to our knowledge it is.
-```</p>
+    tattoo. It is the first entry to become a tattoo isn&#39;t it?</code></pre>
+<p>Landon Curt Noll, the one who told the author about the tattoo, wrote back:</p>
+<pre><code>    Yes, to our knowledge it is.</code></pre>
 <h3 id="regrets">Regrets:</h3>
 <p>Landon Curt Noll wrote that the author regrets not making the program a
 one-liner and not moving the <code>int i</code> into an arg of <code>main()</code> (so that the line