Update years on all the copyrights touched

c++/src/capnp/canonicalize-test.c++

-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Copyright (c) 2016 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

c++/src/capnp/layout.c++

-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Copyright (c) 2013-2016 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

c++/src/capnp/layout.h

-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Copyright (c) 2013-2016 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

c++/src/capnp/message.c++

-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Copyright (c) 2013-2016 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

c++/src/capnp/message.h

-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Copyright (c) 2013-2016 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy