Default to using 2021a tzdata

[omus]

Release notes for tzdata:

• 2020e: https://mm.icann.org/pipermail/tz-announce/2020-December/000063.html
• 2020f: https://mm.icann.org/pipermail/tz-announce/2020-December/000064.html
• 2021a: https://mm.icann.org/pipermail/tz-announce/2021-January/000065.html

Release notes for Unicode CLDR:

• Release 38-1: https://github.com/unicode-org/cldr/releases/tag/release-38-1

[codecov-io]

Codecov Report

Merging #320 (faa208e) into master (dbb756c) will decrease coverage by 1.21%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #320      +/-   ##
==========================================
- Coverage   93.73%   92.51%   -1.22%     
==========================================
  Files          32       32              
  Lines        1532     1510      -22     
==========================================
- Hits         1436     1397      -39     
- Misses         96      113      +17     

Impacted Files	Coverage Δ
src/tzdata/version.jl	91.42% <ø> (ø)
src/winzone/WindowsTimeZoneIDs.jl	0.00% <0.00%> (-79.17%)	⬇️
src/build.jl	83.33% <0.00%> (-16.67%)	⬇️
src/tzdata/archive.jl	100.00% <0.00%> (ø)
src/local.jl	88.88% <0.00%> (+0.73%)	⬆️
src/tzdata/build.jl	68.18% <0.00%> (+4.54%)	⬆️

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