Experiment with the following two commands:
git ls-remote -h -t https://github.com/ably-forks/msgpack-js.git git ls-remote -h -t git://github.com/ably-forks/msgpack-js.git
If the first one works, but the second one just hangs, you're behind a firewall that's blocking the git protocol. You can fix it by telling git to use https instead, by running:
git config --global url."https://github.com/".insteadOf firstname.lastname@example.org: git config --global url."https://".insteadOf git://
Then try installing ably-js again.