Update the favicon in the doc to the new leaf logo.

Take the one used on w.a.o which is a png file, instead of the previous ico file.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1928911 13f79535-47bb-0310-9956-ffa450edef68

Author: Christophe Jaillet

docs/manual/images/favicon.png

@@ -177,7 +177,7 @@
     <script type="text/javascript" src="{$path}/style/scripts/prettify.min.js">&lf;</script>&lf;
     <!-- chm files do not need a favicon -->
     <xsl:if test="not($is-chm or $is-zip)">&lf;
-        <link rel="shortcut icon" href="{$path}/images/favicon.ico" />
+        <link rel="shortcut icon" href="{$path}/images/favicon.png" />
         <xsl:if test="$is-retired">
             <xsl:choose>
             <xsl:when test="$upgrade">