README: Update expected exception when translation not found

[hugovk]

Changes proposed in this pull request:

• Followup to Fix fractional(0.333) output in README #134
• Found via byexample (re: Python 3.8+: NameError: name 'cache' is not defined byexamples/byexample#116)
• Update some test things

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• Just one thing left, which I don't think needs to be runnable:

$ byexample -x-shebang 'python:/Library/Frameworks/Python.framework/Versions/3.8/bin/python3 %a' -l python -o '+force-echo-filtering +geometry=24x300' README.md

**********************************************************************
File "README.md", line 171
Failed example:
    humanize.i18n.activate("pt_BR", path="path/to/my/portuguese/translation/")
Expected:
<gettext.GNUTranslations instance ...>
Got:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/hugo/github/humanize/src/humanize/i18n.py", line 27, in activate
    translation = gettext_module.translation("humanize", path, [locale])
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/gettext.py", line 588, in translation
    raise FileNotFoundError(ENOENT,
FileNotFoundError: [Errno 2] No translation file found for domain: 'humanize'


File README.md, 52/52 test ran in 1.03 seconds
[FAIL] Pass: 51 Fail: 1 Skip: 0

[codecov-commenter]

Codecov Report

Merging #136 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #136   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          416       416           
=========================================
  Hits           416       416           

Flag	Coverage Δ
#GHA_Ubuntu	100.00% <ø> (ø)
#GHA_Windows	100.00% <ø> (ø)
#GHA_macOS	100.00% <ø> (ø)

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