Use shared_path for NPM cache
Use shared_path for NPM cache

I was using `path` beforehand, when it is better to store the cache in a
shared directory.

pghalliday/application_nodejs,gregnorth/application_nodejs,keithlayne/application_nodejs,leonidas/application_nodejs,joraff/application_nodejs,xdv/cookbook-application_nodejs,joraff/application_nodejs,ripple/cookbook-application_nodejs,SupersonicAds/application_nodejs,leonkenneth/application_nodejs,iheartradio/application_nodejs,keithlayne/application_nodejs,pghalliday/application_nodejs,mburns/application_nodejs,mburns/application_nodejs,gravitystorm/application_nodejs,inscitiv/application_nodejs,SupersonicAds/application_nodejs,kewubenduben/application_nodejs,xdv/cookbook-application_nodejs