package/mxml: fix download URL

The project moved to github, the current download URL is broken:

$ wget -q  http://www.msweet.org/files/project3/mxml-2.10.tar.gz
$ file mxml-2.10.tar.gz
mxml-2.10.tar.gz: HTML document, UTF-8 Unicode text, with very long lines

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/mxml/mxml.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 MXML_VERSION = 2.10
-MXML_SITE = http://www.msweet.org/files/project3
+MXML_SITE = https://github.com/michaelrsweet/mxml/releases/download/release-$(MXML_VERSION)
 MXML_LICENSE = LGPL-2.0+ with exceptions
 MXML_LICENSE_FILES = COPYING
 MXML_INSTALL_STAGING = YES