Use new gpl text with updated address

The COPYING file was out of date. The address was not the correct one. I've just replaced it with a new copy of GPLv2. 

I caught this while creating an rpm for Fedora using rpmlint: https://fedoraproject.org/wiki/Common_Rpmlint_issues#incorrect-fsf-address

The review ticket is here https://bugzilla.redhat.com/show_bug.cgi?id=982255