Update copyright line to 2015
diff --git a/library/entropy.c b/library/entropy.c
index 7ce2401..a9d2f1b 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -1,7 +1,7 @@
 /*
  *  Entropy accumulator implementation
  *
- *  Copyright (C) 2006-2011, ARM Limited, All Rights Reserved
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
  *
  *  This file is part of mbed TLS (https://polarssl.org)
  *