Julia Pkg System Maintenance

[ccoffrin]

Here are my suggested updates that I think should resolve issue #59.

I had to relax some of AC-TNEP tests because the solver was finding slightly different solutions on different platforms; there was no dramatic change in the solution quality in those cases.

[codecov-commenter]

Codecov Report

Merging #60 into master will increase coverage by 2.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   58.32%   60.57%   +2.25%     
==========================================
  Files          37       37              
  Lines        3753     3970     +217     
==========================================
+ Hits         2189     2405     +216     
- Misses       1564     1565       +1     

Impacted Files	Coverage Δ
src/prob/acdctnepopf.jl	97.14% <0.00%> (+0.12%)	⬆️
src/prob/mp_acdctnepopf.jl	92.50% <0.00%> (+0.19%)	⬆️
src/prob/acdcopf_bf.jl	97.56% <0.00%> (+0.19%)	⬆️
src/prob/acdcopf.jl	97.43% <0.00%> (+0.21%)	⬆️
src/prob/mp_tnepopf.jl	91.17% <0.00%> (+0.26%)	⬆️
src/prob/acdcpf.jl	92.30% <0.00%> (+0.30%)	⬆️
src/formdcgrid/acp.jl	94.66% <0.00%> (+0.54%)	⬆️
src/core/constraint_template.jl	88.77% <0.00%> (+0.71%)	⬆️
src/core/data.jl	83.79% <0.00%> (+0.85%)	⬆️
src/prob/tnepopf.jl	83.33% <0.00%> (+0.87%)	⬆️
... and 17 more

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