Change the script hook for peerDepInstall task

[agubler]

Currently dojo2 packages use the prepubish to run the grunt task that installs peer dependencies.

As of npm5 this hook it deprecated, we need to find a new hook (or hooks) to run the peer dependency grunt task.

We should consider the prepare hook, but we cannot just swap if we want to still support npm 3+ as the hook was only introduced in npm4