message: Fix the estimator version.
diff: @@ -62,7 +62,7 @@ REQUIRED_PACKAGES = [
  'opt_einsum >= 2.3.2',
  'protobuf >= 3.8.0',
  'tensorboard >= 2.1.0, < 2.2.0',
  - 'tensorflow_estimator >= 2.1.0, < 2.2.0',
  + 'tensorflow_estimator >= 2.1.0rc0, < 2.2.0',
  'termcolor >= 1.1.0',
  'wrapt >= 1.11.1',
  # python3 requires wheel 0.26
  