Reattach the docstring for Future.abs2

[sotashimozono]

This is a trivial documentation issue. The docstring for ColorVectorSpace.Future.abs2 is separated from the definition by a blank line and an intervening if VERSION block, so it is never attached.

julia> using ColorVectorSpace   # v0.11.0

julia> F = ColorVectorSpace.Future;

julia> haskey(Base.Docs.meta(F), Base.Docs.Binding(F, :abs2))
false

Moving the docstring down to function abs2 restores it. Julia binds a string literal to the immediately following expression, and the manual notes that no blank lines or comments may intervene.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.33%. Comparing base (028a3f0) to head (5612e74).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #204   +/-   ##
=======================================
  Coverage   85.33%   85.33%           
=======================================
  Files           3        3           
  Lines         266      266           
=======================================
  Hits          227      227           
  Misses         39       39           

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