Fix bug with division by zero in complex simshow

[roflmaostc]

Hi,

just a division by zero bug which causes hard errors inside Pluto:

# master
julia> simshow(zeros(ComplexF32,(2,2)))
2×2 Array{HSV{Float32},2} with eltype ColorTypes.HSV{Float32}:
 HSV{Float32}(0.0,1.0,NaN)  HSV{Float32}(0.0,1.0,NaN)
 HSV{Float32}(0.0,1.0,NaN)  HSV{Float32}(0.0,1.0,NaN)

# fix
julia> simshow(zeros(ComplexF32,(2,2)))
2×2 Array{HSV{Float32},2} with eltype ColorTypes.HSV{Float32}:
 HSV{Float32}(0.0,1.0,0.0)  HSV{Float32}(0.0,1.0,0.0)
 HSV{Float32}(0.0,1.0,0.0)  HSV{Float32}(0.0,1.0,0.0)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.41%. Comparing base (05ec585) to head (2718586).

❗ Current head 2718586 differs from pull request most recent head ea2d5fb. Consider uploading reports for the commit ea2d5fb to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #59      +/-   ##
==========================================
+ Coverage   88.32%   88.41%   +0.09%     
==========================================
  Files           7        7              
  Lines         257      259       +2     
==========================================
+ Hits          227      229       +2     
  Misses         30       30              

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[roflmaostc]

Maybe we change the CI to Julia 1.6? Seems like some compat issues?