message: Add deprecation notice to tf.contrib.libsvm
  Since tf.contrib has been deprecated and will be removed
  in TF 2.0, it makes sense to add deprecation notice
  so that users could be pointed to tensorflow-io
diff: @@ -22,12 +22,17 @@ from tensorflow.contrib.util import loader
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import sparse_tensor
  from tensorflow.python.platform import resource_loader
  +from tensorflow.python.util.deprecation import deprecated
  _libsvm_ops_so = loader.load_op_library(
  resource_loader.get_path_to_datafile("_libsvm_ops.so"))
  -
  +@deprecated(
  + None,
  + 'tf.contrib.libsvm will be removed in 2.0, the support for libsvm '
  + 'format will continue to be provided in tensorflow-io: '
  + 'https://github.com/tensorflow/io')
  def decode_libsvm(content, num_features, dtype=None, label_dtype=None):
  """Convert Libsvm records to a tensor of label and a tensor of feature.
  