release: Update package.xml version to 1.2.0

package.xml

 <?xml version="1.0"?>
 <package format="3">
   <name>biped_stabilizer</name>
-  <version>1.1.0</version>
+  <version>1.2.0</version>
   <description>Stabilizer for biped locomotion</description>
   <maintainer email="guilhem.saurel@laas.fr">Guilhem Saurel</maintainer>
   <author email="pierre.fernbach@toward.fr">Pierre Fernbach</author>