code: function SyncManager(master, packageToVersions, hostname, root) {
    this.master = master;
    this.packageToVersions = packageToVersions;
    this.hostname = hostname;
    this.root = root;
  }
docs: @constructor
  
  @param {string} master npm registry to get packages from.
  @param {Object} packageToVersions map from package name to object with
  key list of versions we need for the package.
  @param {string} hostname new host that will serve mirrored packages.
  @param {string} root path for mirrored packages.