message: Update tensorboard dep to 1.8.x
diff: @@ -38,7 +38,7 @@ REQUIRED_PACKAGES = [
  'numpy >= 1.13.3',
  'six >= 1.10.0',
  'protobuf >= 3.4.0',
  - 'tensorboard >= 1.7.0, < 1.8.0',
  + 'tensorboard >= 1.8.0, < 1.9.0',
  'termcolor >= 1.1.0',
  ]
  