release: Update package.xml version to 1.3.1

Author: nim65s

package.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <package format="3">
   <name>eiquadprog</name>
-  <version>1.3.0</version>
+  <version>1.3.1</version>
   <description>
     Eiquadprog a QP solver using active sets
   </description>