message: Bump the version of protobuf TF pip package depends on.
  Fixes
diff: @@ -55,7 +55,7 @@ REQUIRED_PACKAGES = [
  'keras_preprocessing >= 1.0.3',
  'numpy >= 1.13.3',
  'six >= 1.10.0',
  - 'protobuf >= 3.6.0',
  + 'protobuf >= 3.6.1',
  'tensorboard >= 1.11.0, < 1.12.0',
  'termcolor >= 1.1.0',
  ]
  