fix CC0 link

index.html

@@ -185,7 +185,7 @@ sudo setup/start.sh</pre>
 
 					<p>Thank you to the contributors!</p>
 
-					<p>Mail-in-a-Box is dedicated to the public domain using [CC0](https://creativecommons.org/publicdomain/zero/1.0/).</p>
+					<p>Mail-in-a-Box is dedicated to the public domain using <a href="https://creativecommons.org/publicdomain/zero/1.0/">CC0</a>.</p>
 
 					<h2>Acknowledgements</h2>