Update Libxml2 require to 2.9+

Olivier Courtin · Olivier Courtin · commit 7b2497f2cbe7 · 2015-06-29T08:54:59.000+02:00
diff --git a/README b/README
@@ -17,5 +17,5 @@ All code must meet the following rules :
 
 Code dynamically linked with the following other librairies:
 - PostgreSQL 8.x and 9.x
-- libxml 2.8.x
+- libxml 2.9.x
 - flex
