bug: test_contrib_wandb.py unit test fails ModuleNotFoundError: No module named 'six.moves.collections_abc'

[jimthompson5802]

Describe the bug
@w4nderlust I noticed that when you merged couple of my PRs, the unit tests tests/integration_tests/test_contrib_wandb.py failed with this error:

==================================== ERRORS ====================================
483________ ERROR collecting tests/integration_tests/test_contrib_wandb.py ________
484ImportError while importing test module '/home/travis/build/uber/ludwig/tests/integration_tests/test_contrib_wandb.py'.
485Hint: make sure your test modules/packages have valid Python names.
486Traceback:
487tests/integration_tests/test_contrib_wandb.py:12: in <module>
488    import wandb
489../../../virtualenv/python3.6.7/lib/python3.6/site-packages/wandb/__init__.py:45: in <module>
490    from wandb.apis import InternalApi, PublicApi, CommError
491../../../virtualenv/python3.6.7/lib/python3.6/site-packages/wandb/apis/__init__.py:97: in <module>
492    from .file_stream import FileStreamApi
493../../../virtualenv/python3.6.7/lib/python3.6/site-packages/wandb/apis/file_stream.py:11: in <module>
494    from wandb import util
495../../../virtualenv/python3.6.7/lib/python3.6/site-packages/wandb/util.py:46: in <module>
496    from wandb import wandb_config
497../../../virtualenv/python3.6.7/lib/python3.6/site-packages/wandb/wandb_config.py:2: in <module>
498    from six.moves.collections_abc import Sequence
499E   ModuleNotFoundError: No module named 'six.moves.collections_abc'
500!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
501=========================== 1 error in 3.80 seconds ============================

To Reproduce
Steps to reproduce the behavior:
Submit PR

Expected behavior
Unit test should not fail

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):
Travis-ci environment
and my local docker container

• OS: [e.g. iOS] MacOS 10.15.3
• Docker for Mac: 2.2.0.0
• Python version: Py 3.6
• Ludwig version 2.1

Additional context
Failure due mis-match dependency between package six 1.11.0 and wandb 0.8.26, which became available on PyPi on 10Feb. Version wandb 0.8.26 requires six 1.13.0. However, the environment build installs six 1.11.0.

One possible fix is to add six==1.13.0 to requirements_test.txt. I've tested this locally and all unit tests pass.

# pip list | grep wandb
wandb                0.8.26
# pip list | grep six
six                  1.13.0
# pytest tests
============================= test session starts ==============================
platform linux -- Python 3.6.9, pytest-5.3.5, py-1.8.1, pluggy-0.13.1
rootdir: /opt/project
collected 81 items

../../tests/integration_tests/test_api.py .                              [  1%]
../../tests/integration_tests/test_contrib_wandb.py .                    [  2%]
../../tests/integration_tests/test_experiment.py ...................     [ 25%]
../../tests/integration_tests/test_kfold_cv.py ...                       [ 29%]
../../tests/integration_tests/test_server.py .                           [ 30%]
../../tests/integration_tests/test_visualization.py .................... [ 55%]
......                                                                   [ 62%]
../../tests/integration_tests/test_visualization_api.py ................ [ 82%]
......                                                                   [ 90%]
../../tests/ludwig/models/modules/test_encoder.py ....                   [ 95%]
../../tests/ludwig/utils/test_data_utils.py .                            [ 96%]
../../tests/ludwig/utils/test_image_utils.py ..                          [ 98%]
../../tests/ludwig/utils/test_normalization.py .                         [100%]

=============================== warnings summary ===============================
<<<< DELETED WARNING LINES >>>>>>>>
================ 81 passed, 7480 warnings in 488.79s (0:08:08) =================

If this seems reasonable, I can submit a PR