Install the offical Github cli tool from here, login, and then dump all gists:
gh auth login
mkdir ~/gists
cd ~/gists
gh gist list | awk '{print $1}' | xargs -I{} gh gist clone {}
to update them:
cd ~/gists
find . -not -path "./gisthub-bu" -mindepth 1 -maxdepth 1 -type d -print -exec git -C {} pull --ff-only \;