community/py3-img2pdf: upgrade to 0.3.4
Also add Python 3 as a dependency so that /usr/bin/img2pdf doesn't exit
with sh: img2pdf: not found
. Before this change the command below
exits with that error message:
docker run --rm -ti alpine:edge \
sh -c "apk upgrade && apk add py3-img2pdf && img2pdf --version"