debian/copyright: Adding my employer

This aims at invalidating the REJECT reason provided by Debian's ftp-master:

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Dear maintainer,

unfortunately I have to recject your package.

The source file header says that the copyright holder is:
  Copyright (C) 2013 Astaro GmbH & Co. KG  -- a Sophos company

As opposed to this debian/copyright says that you hold the
copyright.

This doesn't seem to be correct.

Best regards
Thorsten

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