[wp] Fix wrong header in MemRegion

src/plugins/wp/MemRegion.ml

-(*************************************************************************)
+(**************************************************************************)
 (*                                                                        *)
 (*  This file is part of WP plug-in of Frama-C.                           *)
 (*                                                                        *)
@@ -18,7 +18,7 @@
 (*  See the GNU Lesser General Public License version 2.1                 *)
 (*  for more details (enclosed in the file licenses/LGPLv2.1).            *)
 (*                                                                        *)
-(*************************************************************************)
+(**************************************************************************)
 
 (* -------------------------------------------------------------------------- *)
 (* --- Region Memory Model                                                --- *)