To update the timezone data, download the latest from iana:

https://www.iana.org/time-zones

Remove the entire tzdata directory, then untar the data file
into there and add the contents:

e.g.

git clean -f -x -d
git rm -r tzdata
mkdir tzdata
tar -C tzdata -x -f /tmp/tzdata2018e.tar.gz
git add tzdata
git commit -m 'tzdata2018e'

