Only return alpha in _hzI12

[anriseth]

Fixes #123

[codecov]

Codecov Report

Merging #124 into master will increase coverage by 0.82%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #124      +/-   ##
==========================================
+ Coverage   60.36%   61.19%   +0.82%     
==========================================
  Files           8        8              
  Lines         651      652       +1     
==========================================
+ Hits          393      399       +6     
+ Misses        258      253       -5

Impacted Files	Coverage Δ
src/initialguess.jl	85.71% <100%> (+6.19%)	⬆️

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