Use "kB" for DownloadColumn

[bhrutledge]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

While working on pypa/twine#877, I noticed that DownloadColumn uses KB instead of kB, even though the divisor is 1000 (like FileSizeColumn and TransferSpeedColumn).

[codecov-commenter]

Codecov Report

Merging #1986 (156c9c4) into master (e839bfb) will decrease coverage by 0.01%.
The diff coverage is 99.09%.

@@            Coverage Diff             @@
##           master    #1986      +/-   ##
==========================================
- Coverage   99.82%   99.81%   -0.02%     
==========================================
  Files          71       71              
  Lines        6943     7043     +100     
==========================================
+ Hits         6931     7030      +99     
- Misses         12       13       +1     

Flag	Coverage Δ
unittests	99.81% <99.09%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
rich/default_styles.py	100.00% <ø> (ø)
rich/highlighter.py	100.00% <ø> (ø)
rich/markdown.py	100.00% <ø> (ø)
rich/syntax.py	99.27% <97.72%> (-0.34%)	⬇️
rich/pretty.py	99.71% <98.88%> (-0.29%)	⬇️
rich/__main__.py	100.00% <100.00%> (ø)
rich/_inspect.py	100.00% <100.00%> (ø)
rich/color.py	100.00% <100.00%> (ø)
rich/console.py	100.00% <100.00%> (ø)
rich/filesize.py	100.00% <100.00%> (ø)
... and 6 more

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[willmcgugan]

Thanks