Minor bug fix for allowing an extension of const-qualified types in containers.

llvm-svn: 183481
diff --git a/libcxx/include/memory b/libcxx/include/memory
index 912a43f..bcf4d6d 100644
--- a/libcxx/include/memory
+++ b/libcxx/include/memory
@@ -1750,7 +1750,7 @@
     typedef const _Tp*        const_pointer;
     typedef const _Tp&        reference;
     typedef const _Tp&        const_reference;
-    typedef _Tp               value_type;
+    typedef const _Tp         value_type;
 
     typedef true_type propagate_on_container_move_assignment;