Update copyright year to 2015.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@232094 91177308-0d34-0410-b5e6-96231b3b80d8

LICENSE.TXT

@@ -14,7 +14,7 @@ Full text of the relevant licenses is included below.
 University of Illinois/NCSA
 Open Source License
 
-Copyright (c) 2009-2014 by the contributors listed in CREDITS.TXT
+Copyright (c) 2009-2015 by the contributors listed in CREDITS.TXT
 
 All rights reserved.