CSS: margin 'none' -> '0'.

After this change the CSS validates on jigsaw.w3.org.

Reported by Anonymous on SourceForge bug #2886542.

gitstats.css

 .nav ul {
 	list-style-type: none;
 	display: inline;
-	margin: none;
+	margin: 0;
 	padding: 0;
 }