EventEmitter memory leak

[brunosan]

When running large regions e.g. http://geojson.io/#id=gist:anonymous/2df11d88af2da288e15c&map=8/7.648/-10.712

(node) warning: possible EventEmitter memory leak detected. 11 listeners added.
 Use emitter.setMaxListeners() to increase limit.
Trace
    at WriteStream.EventEmitter.addListener (events.js:160:15)
    at /mnt/data/tiles/tile-cover.js:24:10
    at Array.forEach (native)
    at Object.<anonymous> (/mnt/data/tiles/tile-cover.js:21:15)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)