message: Add back spec that got lost somehow
diff: @@ -271,6 +271,7 @@ def uberenv_create_mirror(prefix, spec, project_file, mirror_path):
  assertUberenvExists()
  cmd = "python {0} --create-mirror -k ".format(get_uberenv_path())
  cmd += " --prefix=\"{0}\" --mirror=\"{1}\"".format(prefix, mirror_path)
  + cmd += "--spec=\"{0}\" ".format(spec)
  if project_file:
  cmd += " --project-json=\"{0}\" ".format(project_file)
  