fix: (locale: bg) correct abbreviations & more common plural forms

[TonyBogdanov]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (f68e4b1) to head (bd85a69). Report is 193 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #1612   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          177       177           
  Lines         1989      1989           
  Branches       505       505           
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  Hits          1989      1989           

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[iamkun]

seems these's some different with https://github.com/moment/moment/blob/develop/locale/bg.js

[TonyBogdanov]

@iamkun Because that one's incorrect as well. I've just pushed a PR there too: https://github.com/moment/moment/pull/5930