Migrate to new kind-projector symbol

[LukaJCB]

We're going to deprecate the use of ? soon and we have * as a replacement for now. See this issue: typelevel/kind-projector#108

See here for the overall migration strategy: http://dotty.epfl.ch/docs/reference/changed-features/wildcards.html

[codecov-io]

Codecov Report

Merging #2929 into master will not change coverage.
The diff coverage is 99.07%.

@@           Coverage Diff           @@
##           master    #2929   +/-   ##
=======================================
  Coverage   94.03%   94.03%           
=======================================
  Files         370      370           
  Lines        7038     7038           
  Branches      186      186           
=======================================
  Hits         6618     6618           
  Misses        420      420

Impacted Files	Coverage Δ
core/src/main/scala/cats/ApplicativeError.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/either.scala	86.76% <ø> (ø)	⬆️
core/src/main/scala/cats/Bifunctor.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/data/EitherK.scala	93.18% <ø> (ø)	⬆️
.../src/main/scala/cats/syntax/applicativeError.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/FlatMap.scala	86.66% <ø> (ø)	⬆️
core/src/main/scala/cats/Applicative.scala	95% <ø> (ø)	⬆️
core/src/main/scala/cats/data/Op.scala	87.5% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/TrySyntax.scala	100% <ø> (ø)	⬆️
core/src/main/scala/cats/syntax/option.scala	100% <ø> (ø)	⬆️
... and 50 more

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