Use poly lambda syntax in FreeApplicative test

[ceedubs]

This is the last explicit new FunctionK that I saw in the code base
when I looked to close out #1374.

[codecov-io]

Codecov Report

Merging #2213 into master will increase coverage by 0.2%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #2213     +/-   ##
=========================================
+ Coverage   94.83%   95.04%   +0.2%     
=========================================
  Files         333      333             
  Lines        5789     5789             
  Branches      211      211             
=========================================
+ Hits         5490     5502     +12     
+ Misses        299      287     -12

Impacted Files	Coverage Δ
core/src/main/scala/cats/instances/vector.scala	100% <0%> (+27.27%)	⬆️

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[peterneyens]

There are a few more using ~> in CofreeSuite.

[ceedubs]

Good catch @peterneyens. Updated.

[peterneyens]

Sorry for not linking to them in my previous comment, but there are also toList and inclusion in CofreeSuite. (inclusion could be OptionT.liftK[Eval] I think).

[ceedubs]

@peterneyens yet another good catch. Updated again.