code: function update(id, packagePath, keepFile) {
          return Package.installUpdate(packagePath, id).done(function () {
              if (!keepFile) {
                  FileSystem.getFileForPath(packagePath).unlink();
              }
          });
      }
docs: Updates an installed extension with the given package file.
  @param {string} id of the extension
  @param {string} packagePath path to the package file
  @param {boolean=} keepFile Flag to keep extension package file, default=false
  @return {$.Promise} A promise that's resolved when the extension is updated or
  rejected with an error if there's a problem with the update.