convert types in kron multiply

[dpo]

fixes #110

[codecov]

Codecov Report

Merging #124 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #124      +/-   ##
==========================================
+ Coverage   96.23%   96.25%   +0.01%     
==========================================
  Files           7        7              
  Lines         585      588       +3     
==========================================
+ Hits          563      566       +3     
  Misses         22       22

Impacted Files	Coverage Δ
src/kron.jl	100% <100%> (ø)	⬆️

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[abelsiqueira]

Thank you