Upgrade production node version to v0.10.24

As @evdb predicted in #275, the new `npm-shrinkwrap.json` doesn't work with the node version on the server. It seems the best thing to do is update the node version on the server. Currently we're using v0.8.4 (released July 2012), this change brings us up to the latest v0.10 patch release.

If the currently installed node version on the server doesn't match the configured version, it will be upgraded in place.

This change switches to using the pre-built linux binaries from nodejs.org, which significantly reduces the install time for a new version of node (because we no longer have to compile node from source). Hopefully this will encourage us to upgrade more frequently in the future.

Closes #276