Fix syntax highlighting in the reference documentation

Closes gh-16548

Author: wilkinsona

spring-boot-docs/src/main/docbook/xsl/common.xsl

@@ -20,7 +20,7 @@
 -->
 
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-		xmlns:xslthl="http://xslthl.sourceforge.net/"
+		xmlns:xslthl="http://xslthl.sf.net"
 		xmlns:d="http://docbook.org/ns/docbook"
 		exclude-result-prefixes="xslthl d"
 		version='1.0'>

spring-boot-docs/src/main/docbook/xsl/epub.xsl

@@ -20,7 +20,7 @@ under the License.
 -->
 
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-		xmlns:xslthl="http://xslthl.sourceforge.net/"
+		xmlns:xslthl="http://xslthl.sf.net"
 		xmlns:d="http://docbook.org/ns/docbook"
 		exclude-result-prefixes="xslthl d"
 		version='1.0'>

spring-boot-docs/src/main/docbook/xsl/html.xsl

@@ -20,7 +20,7 @@ under the License.
 -->
 
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-		xmlns:xslthl="http://xslthl.sourceforge.net/"
+		xmlns:xslthl="http://xslthl.sf.net"
 		xmlns:d="http://docbook.org/ns/docbook"
 		exclude-result-prefixes="xslthl"
 		version='1.0'>

spring-boot-docs/src/main/docbook/xsl/pdf.xsl

@@ -22,7 +22,7 @@ under the License.
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 				xmlns:d="http://docbook.org/ns/docbook"
 				xmlns:fo="http://www.w3.org/1999/XSL/Format"
-				xmlns:xslthl="http://xslthl.sourceforge.net/"
+				xmlns:xslthl="http://xslthl.sf.net"
 				xmlns:xlink='http://www.w3.org/1999/xlink'
 				xmlns:exsl="http://exslt.org/common"
 				exclude-result-prefixes="exsl xslthl d xlink"

spring-boot-docs/src/main/docbook/xsl/xslthl-config.xml

@@ -19,5 +19,5 @@
 	<highlighter id="properties" file="./xslthl/properties-hl.xml" />
 	<highlighter id="json" file="./xslthl/json-hl.xml" />
 	<highlighter id="yaml" file="./xslthl/yaml-hl.xml" />
-	<namespace prefix="xslthl" uri="http://xslthl.sourceforge.net/" />
+	<namespace prefix="xslthl" uri="http://xslthl.sf.net" />
 </xslthl-config>