check to see if a file has changed since another file has been changed. useful for refreshing cache files.
var shouldChange = require('file-should-change')
// all.json gets updated at an interval
// week.json it the last week of changes which i need to update each time all.json gets updated
shouldChange('week.json','all.json',function(err,shouldChange){
})
// you can also pass a unixtimestamp in ms as a number instead of another file.
shouldChange('week.json',number timestamp ,function(err,shouldChange){
})