message: updated for tf2.0
  This didn't work for me with 1.14 and with 2.0. Otherwise it with this class.
diff: ```python
  >>> import os
  ->>> import tensorflow as tf
  +>>> import tensorflow as tf # Assuming TensorFlow >= 2.0
  >>> import tensorflow_io as tfio
  >>>
  >>> os.environ['TF_AZURE_STORAGE_KEY'] = 'my-storage-key'
  >>>
  ->>> with tf.gfile.Open("az://myaccount/mycontainer/hello.txt", mode='w') as w:
  +>>> with tf.io.gfile.GFile("az://myaccount/mycontainer/hello.txt", mode='w') as w:
  >>> w.write("Hello, world!")
  >>>
  ->>> with tf.gfile.Open("az://myaccount/mycontainer/hello.txt", mode='r') as r:
  +>>> with tf.io.gfile.GFile("az://myaccount/mycontainer/hello.txt", mode='r') as r:
  >>> print(r.read())
  Hello, world!
  ```
  -
  ## TODO
  - Support OAuth
  