change test files that do not end in .txt to view via GitHub

1988/isaak/index.html

@@ -208,7 +208,7 @@ file: isaak.encode. To read this file do.</p>
 <li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/isaak/Makefile">Makefile</a> - entry Makefile</li>
 <li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/isaak/isaak.alt.c">isaak.alt.c</a> - alternative source</li>
 <li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/isaak/isaak.orig.c">isaak.orig.c</a> - original source</li>
-<li><a href="isaak.encode">isaak.encode</a> - uuencoded sample output</li>
+<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/isaak/isaak.encode">isaak.encode</a> - uuencoded sample output</li>
 </ul>
 <h2 id="secondary-files">Secondary files</h2>
 <ul>