add Tuple2K#swap

[aoiroaoino]

No description provided.

[codecov-io]

Codecov Report

Merging #2367 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2367      +/-   ##
==========================================
+ Coverage   95.01%   95.01%   +<.01%     
==========================================
  Files         349      349              
  Lines        5997     5998       +1     
  Branches      223      221       -2     
==========================================
+ Hits         5698     5699       +1     
  Misses        299      299

Impacted Files	Coverage Δ
core/src/main/scala/cats/data/Tuple2K.scala	91.3% <100%> (+0.19%)	⬆️

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[kailuowang]

Thanks

[LukaJCB]

Thanks @aoiroaoino :)