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 git@github.com:
git config --global url."https://".insteadOf git://

Then try installing ably-js again.