make type parameters convert correctly

[GiggleLiu]

No description provided.

[codecov]

Codecov Report

Merging #80 (62388fd) into master (9f7edcf) will increase coverage by 0.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #80      +/-   ##
==========================================
+ Coverage   83.11%   83.31%   +0.19%     
==========================================
  Files          30       30              
  Lines        1558     1564       +6     
==========================================
+ Hits         1295     1303       +8     
+ Misses        263      261       -2     

Impacted Files	Coverage Δ
src/autodiff/vars.jl	78.63% <100.00%> (+1.15%)	⬆️
src/complex.jl	69.36% <0.00%> (+1.80%)	⬆️

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