message: Update metadata of setup.py
  This PR updates  metadata of setup.py to specify python versions, and enhance
  classifiers to align with tensorflow core repo.
diff: @@ -151,6 +151,8 @@ setup(
  name=project_name,
  version=__version__,
  description=('TensorFlow IO'),
  + url='https://github.com/tensorflow/io',
  + download_url='https://github.com/tensorflow/io/tags',
  author='Google Inc.',
  author_email='opensource@google.com',
  # Contained modules and scripts.
  @@ -168,12 +170,18 @@ setup(
  'Intended Audience :: Education',
  'Intended Audience :: Science/Research',
  'License :: OSI Approved :: Apache Software License',
  - 'Programming Language :: Python :: 2.7',
  + 'Programming Language :: Python :: 3',
  'Programming Language :: Python :: 3.5',
  'Programming Language :: Python :: 3.6',
  + 'Programming Language :: Python :: 3.7',
  + 'Programming Language :: Python :: 3.8',
  + 'Programming Language :: Python :: 3 :: Only',
  + 'Topic :: Scientific/Engineering',
  'Topic :: Scientific/Engineering :: Mathematics',
  - 'Topic :: Software Development :: Libraries :: Python Modules',
  + 'Topic :: Scientific/Engineering :: Artificial Intelligence',
  + 'Topic :: Software Development',
  'Topic :: Software Development :: Libraries',
  + 'Topic :: Software Development :: Libraries :: Python Modules',
  ],
  license='Apache 2.0',
  keywords='tensorflow io machine learning',
  