package/libxml2: add license hash

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/libxml2/libxml2.hash

@@ -1,2 +1,4 @@
 # Locally calculated after checking pgp signature
 sha256	4031c1ecee9ce7ba4f313e91ef6284164885cdb69937a123f6a83bb6a72dcd38	libxml2-2.9.5.tar.gz
+# License files, locally calculated
+sha256	c5c63674f8a83c4d2e385d96d1c670a03cb871ba2927755467017317878574bd	COPYING