Should add lodash as a dependency

Lodash is required in [./files/stat.js](https://github.com/ipfs/js-ipfs-api/blob/master/src/files/stat.js) and [./pin/ls.js](https://github.com/ipfs/js-ipfs-api/blob/master/src/pin/ls.js) but is not referenced in package.json;

This is causing errors when the core project doesn't require lodash.