[ci] Fix node job
[ci] Fix node job

It seems that we have to use the focal travis-ci image to get a working
node install - on the others node fails to run with errors like:

node: /lib/aarch64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found (required by node)

snowballstem/snowball,snowballstem/snowball,snowballstem/snowball,snowballstem/snowball,snowballstem/snowball,snowballstem/snowball,snowballstem/snowball,snowballstem/snowball