preinstall: update peerDeps before global install

Using node as a portable scripting language, install adequate versions
of our peerDependencies globally when we are installed globally
ourselves.

A normal global install will do this for us, but only on the initial
install. By doing this ourselves in a `preinstall` we can update the
peerDependencies during an `npm update -g strong-cli`.
update: Remove peerDependencies installation

Updating of `peerDependencies` is now down with a `preinstall` npm
lifecycle script.