[Package.xml] Update maintainer, fix #70

Author: nim65s

package.xml

@@ -5,7 +5,7 @@
   <description>
     Dynamic graph library Python bindings
   </description>
-  <maintainer email="ostasse@laas.fr">Olivier Stasse</maintainer>
+  <maintainer email="guilhem.saurel@laas.fr">Guilhem Saurel</maintainer>
   <license>BSD</license>
 
   <url>http://github.com/stack-of-tasks/dynamic-graph-python</url>