[css-step-sizing] Fix links

Fixes w3c#235

Author: kojiishi

css-step-sizing/Overview.bs

@@ -271,7 +271,7 @@ to adjust heights of block-level boxes.
   text inside the <code>&lt;h2&gt;</code> uses ''line-height: 1.2'', while
   the height of the <code>&lt;h2&gt;</code> block is rounded up
   to the multiple of ''18pt''.
-  See <a href="examples/line-height-step.html">a sample in action</a>.
+  See <a href="examples/snap-height.html">a sample in action</a>.
 </div>
 
 Stepping Widths: the 'inline-size-step' property {#width}