Only upload updated package metadata

[jbuck]

{ id: 'lightjs', add: [], remove: [] }
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs/0.0.1 returned HTTP 200
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs returned HTTP 200
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs/0.0.2 returned HTTP 200
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs/0.0.0 returned HTTP 200
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs/latest returned HTTP 200
PUT https://npm-readonly-mirror.s3.amazonaws.com/lightjs/0.0.3 returned HTTP 200
processed {"seq":833270,"id":"lightjs","changes":[{"rev":"62-73ebf744e14870be4857718e887d3c57"}],"retry_count":0}

When a package is updated we have the source and sink versions available to compare. If a versions metadata hasn't been updated, then we don't need to upload it.