code: function mergeFeatureCollectionStream (inputs) {
      var out = geojsonStream.stringify();
      inputs.forEach(function(file) {
          fs.createReadStream(file)
              .pipe(geojsonStream.parse())
              .pipe(out);
      });
      return out;
  }
docs: Merge GeoJSON files containing GeoJSON FeatureCollections
  into a single stream of a FeatureCollection as a JSON string.
  
  This is more limited than merge - it only supports FeatureCollections
  as input - but more performant, since it can operate on GeoJSON files
  larger than what you can keep in memory at one time.
  @param {Array<string>} inputs a list of filenames of GeoJSON files
  @returns {Stream} output: a stringified JSON of a FeatureCollection.
  @example
  var geojsonMerge = require('@mapbox/geojson-merge');
  
  var mergedStream = geojsonMerge.mergeFeatureCollectionStream([
  'features.geojson',
  'otherFeatures.geojson'])
  
  mergedStream.pipe(process.stdout);