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update copyright statement

libcellml/buildbot-testing,hsorby/libcellml,cellml/libcellml,cellml/libcellml,hsorby/libcellml,MichaelClerx/libcellml,cellml/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,MichaelClerx/libcellml,nickerso/libcellml,libcellml/buildbot-testing,nickerso/libcellml,nickerso/libcellml,MichaelClerx/libcellml,nickerso/libcellml