Add more contributors' names.

Cabal/LICENSE

-Copyright (c) 2003-2008, Isaac Jones, Simon Marlow, Martin Sjögren,
+Copyright (c) 2003-2014, Isaac Jones, Simon Marlow, Martin Sjögren,
                          Bjorn Bringert, Krasimir Angelov,
                          Malcolm Wallace, Ross Patterson, Ian Lynagh,
-                         Duncan Coutts, Thomas Schilling
+                         Duncan Coutts, Thomas Schilling,
+                         Johan Tibell, Mikhail Glushenkov
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