fix: use shutil.get_terminal_size instead of os.get_terminal_size

[chrisburr]

os.get_terminal_size fail when there is no terminal connected (e.g. CI):

+ hist --help
Traceback (most recent call last):
  File "/home/conda/staged-recipes/build_artifacts/hist_1601700363608/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_p/bin/hist", line 11, in <module>
    sys.exit(main())
  File "/home/conda/staged-recipes/build_artifacts/hist_1601700363608/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_p/lib/python3.7/site-packages/hist/classichist.py", line 21, in main
    default=os.get_terminal_size()[0],
OSError: [Errno 25] Inappropriate ioctl for device

Using shutil.get_terminal_size instead allows a fallback to be used instead of crashing.

See this build log from conda-forge for a demonstration:
https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=217306&view=logs&jobId=10bda42a-d420-5c28-a43f-bc4e66405e5c&j=10bda42a-d420-5c28-a43f-bc4e66405e5c&t=bef775d0-a1a2-55a3-9721-17147029baf0

[LovelyBuggies]

Thanks :)