Fixes the following error when running the tests on Python 3.

    Traceback (most recent call last):
      File "seq2seq/seq2seq/test/hooks_test.py", line
      55, in test_begin
          self.assertEqual(file_contents.decode(), ...)
          AttributeError: 'str' object has no attribute 'decode'

distutils.version isn't available on the CI versions, so change the test
to not rely explicitly on the version of TensorFlow installed.

…tion

Use of `tf.name_scope` and `tf.variable_scope` cause pylint errors on TF1.2
due to pylint not fully understanding the `tf_contextlib.contextmanager`
decorators.

Following some changes in TF to the `LazyLoader` [1], pylint complains
about not being able to find some imports under `tf.contrib`. This looks
like a pylint issue, emitting errors like:

    ************* Module seq2seq.encoders.rnn_encoder
    E: 24, 0: No name 'rnn' in module 'LazyLoader' (no-name-in-module)
    ************* Module seq2seq.data.input_pipeline
    E: 32, 0: No name 'slim' in module 'LazyLoader' (no-name-in-module)

[1] tensorflow/tensorflow@95c5d7e

…into Add-Docker