[CI.Lint.Black] Use "en_US.UTF-8" for Red Hat 6&7 Compatibility

[Johnson9009]

Lots of company use Red Hat Enterprise Linux servers, for RHEL 6 & 7 there isn't "C.UTF-8" locale, and from the bug tracking https://bugzilla.redhat.com/show_bug.cgi?id=1361965, it seems it's hard to fix this bug in RHEL 6 & 7 soon.

[Johnson9009]

@mehrdadh @tqchen Please help to review, thanks.

[grant-arm]

@Johnson9009 @tqchen This PR appears to have broken CI

Click discovered that you exported a UTF-8 locale but the locale system could not pick up from it because it does not exist. The exported locale is 'en_US.UTF-8' but it is not supported.

Version Information: 

Read returned 0

Files: python/tvm/relay/backend/contrib/ethosu/codegen.py
Running black in checking mode
Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.6/dist-packages/black/__main__.py", line 3, in <module>
    patched_main()
  File "/usr/local/lib/python3.6/dist-packages/black/__init__.py", line 6607, in patched_main
    main()
  File "/usr/local/lib/python3.6/dist-packages/click/core.py", line 1137, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/click/core.py", line 1043, in main
    _verify_python_env()
  File "/usr/local/lib/python3.6/dist-packages/click/_unicodefun.py", line 100, in _verify_python_env
    raise RuntimeError("\n\n".join(extra))
RuntimeError: Click will abort further execution because Python was configured to use ASCII as encoding for the environment. Consult https://click.palletsprojects.com/unicode-support/ for mitigation steps.

This system supports the C.UTF-8 locale which is recommended. You might be able to resolve your issue by exporting the following environment variables:

    export LC_ALL=C.UTF-8
    export LANG=C.UTF-8

[tqchen]

Good catch, this is reverted for now, let us find a better way to set it @Johnson9009 and send another pR