ChangeLog: mention git revision for 1.2.6

ChangeLog

@@ -133,7 +133,7 @@ Small changes:
     scheduler context
   * Fonction starpu_is_initialized() is moved to the public API.
 
-StarPU 1.2.6 (git revision xxx)
+StarPU 1.2.6 (git revision 23049adea01837479f309a75c002dacd16eb34ad)
 ==============================================
 
 Small changes: