feat(Flag): export names in typings

[layershifter]

Fixes #2956.

[codecov-io]

Codecov Report

Merging #2957 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2957   +/-   ##
=======================================
  Coverage   99.78%   99.78%           
=======================================
  Files         161      161           
  Lines        2765     2765           
=======================================
  Hits         2759     2759           
  Misses          6        6

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[levithomason]

Released in semantic-ui-react@0.81.3.