Bump copyright years of files changed in 2019
Done via the following command: git diff 1e6c102b --stat --name-only | cat - | xargs sed -i 's/2017-2018 Pleroma Authors/2017-2019 Pleroma Authors/'
Done via the following command: git diff 1e6c102b --stat --name-only | cat - | xargs sed -i 's/2017-2018 Pleroma Authors/2017-2019 Pleroma Authors/'