code: function locateSeeds(sources, cwd) {
    sources = sources || [];
    cwd = cwd || process.cwd();
  
    const locations = sources.map((source) => path.join(cwd, source));
    return BbPromise.map(locations, (location) => {
      return fileExists(location).then((exists) => {
        if(!exists) {
          throw new Error("source file " + location + " does not exist");
        }
        return getSeedsAtLocation(location);
      });
    // Smash the arrays together
    }).then((seedArrays) => [].concat.apply([], seedArrays));
  }
docs: Locates seeds given a set of files to scrape
  @param {string[]} sources The filenames to scrape for seeds