message: Use environment markers for enum34
  This fix tries to addres the issue raised in 30200 where
  enum34 caused poetry breaks due to the conditional sys.version_info
  This fix changes to use environment markers for enum34 (conform to PEP508)
  This fix fixes 30200.
diff: @@ -52,6 +52,8 @@ _VERSION = '1.14.0'
  REQUIRED_PACKAGES = [
  'absl-py >= 0.7.0',
  'astor >= 0.6.0',
  + 'backports.weakref >= 1.0rc1;python_version<"3.4"',
  + 'enum34 >= 1.1.6;python_version<"3.4"',
  'gast >= 0.2.0',
  'google_pasta >= 0.1.6',
  'keras_applications >= 1.0.8',
  @@ -97,11 +99,6 @@ if 'tf_nightly' in project_name:
  elif 'tensorflow_estimator' in pkg:
  REQUIRED_PACKAGES[i] = 'tf-estimator-nightly'
  -# weakref.finalize and enum were introduced in Python 3.4
  -if sys.version_info < (3, 4):
  - REQUIRED_PACKAGES.append('backports.weakref >= 1.0rc1')
  - REQUIRED_PACKAGES.append('enum34 >= 1.1.6')
  -
  # pylint: disable=line-too-long
  CONSOLE_SCRIPTS = [
  'toco_from_protos = tensorflow.lite.toco.python.toco_from_protos:main',
  