Fix sign bug in BFA formulation

[ccoffrin]

No description provided.

[codecov]

Codecov Report

Merging #780 (509352e) into master (7b62b50) will increase coverage by 0.65%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #780      +/-   ##
==========================================
+ Coverage   93.06%   93.71%   +0.65%     
==========================================
  Files          42       42              
  Lines        9038     8975      -63     
==========================================
  Hits         8411     8411              
+ Misses        627      564      -63     

Impacted Files	Coverage Δ
src/form/bf.jl	100.00% <100.00%> (+1.86%)	⬆️
src/io/pti.jl	90.34% <0.00%> (+0.28%)	⬆️
src/util/obbt.jl	90.79% <0.00%> (+0.37%)	⬆️
src/core/constraint_template.jl	95.38% <0.00%> (+0.54%)	⬆️
src/io/psse.jl	97.14% <0.00%> (+0.63%)	⬆️
src/core/constraint.jl	92.06% <0.00%> (+0.72%)	⬆️
src/form/acr.jl	98.47% <0.00%> (+0.74%)	⬆️
src/core/variable.jl	96.37% <0.00%> (+0.82%)	⬆️
src/core/ref.jl	89.21% <0.00%> (+0.86%)	⬆️
src/core/data.jl	91.92% <0.00%> (+0.87%)	⬆️
... and 8 more

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