Fix link to Scala API
<a name="log4j-api-scala" />
<h4>log4j-api-scala</h4>
<p>
- The Log4j <a href="log4j-api-scala_2.12/index.html">Scala API</a> requires Scala runtime library and reflection in
+ The Log4j <a href="manual/scala-api.html">Scala API</a> requires Scala runtime library and reflection in
addition to the Log4j API.
</p>
