Add object reducible for reducible syntax

[markus1189]

Seems like there is no object for cats.syntax.reducible ;)

[codecov-io]

Current coverage is 90.87%

Merging #985 into master will not affect coverage as of 402ac2d

@@            master    #985   diff @@
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  Files          181     181       
  Stmts         2160    2160       
  Branches        42      42       
  Methods          0       0       
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  Hit           1963    1963       
  Partial          0       0       
  Missed         197     197       

Review entire Coverage Diff as of 402ac2d

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[adelbertc]

Hm did we just have the trait there and have no corresponding object for it? That's strange.. 👍

[fthomas]

👍