update copyright date

We did not intend to imply our copyrights last forever

Closes #759

hphp/runtime/base/array/hphp_array.cpp

@@ -2,7 +2,7 @@
    +----------------------------------------------------------------------+
    | HipHop for PHP                                                       |
    +----------------------------------------------------------------------+
-   | Copyright (c) 2010- Facebook, Inc. (http://www.facebook.com)         |
+   | Copyright (c) 2010-2013 Facebook, Inc. (http://www.facebook.com)     |
    +----------------------------------------------------------------------+
    | This source file is subject to version 3.01 of the PHP license,      |
    | that is bundled with this package in the file LICENSE, and is        |