Remove the bower postinstall step from package.json.

We are already keeping bower_components in the repository so there's no
need for it; also, programs like appchef that want to include appmaker as
a dependency can't run bower as root (which is done when npm -g is used).
Merge pull request #732 from toolness/develop

Remove the bower postinstall step from package.json. -- Installed bower packages are added to git in public/vendor.