Upgrade Tensorflow version to 1.13.1

[josh-taylr]

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[josh-taylr]

I'm going to need some help to understand why CI failed. What I am reading in the logs is that the spec tests passed 🤔

[yebrahim]

Seems like flake8 has failed on the cli directory, probably because of a version change in the tool:

$ flake8 cli/
cli/datalab.py:409:12: F632 use ==/!= to compare str, bytes, and int literals
The command "flake8 cli/" exited with 1.

I'll send a separate PR to fix that.

EDIT
Created #2122.

[yebrahim]

This should be fixed now, can you rebase this PR @josh-taylr?