sum parsing correction and tests

[codecov[bot]]

Codecov Report

Merging #357 (181e583) into master (5657f28) will increase coverage by 0.20%. The diff coverage is 25.80%.

@@            Coverage Diff             @@
##           master     #357      +/-   ##
==========================================
+ Coverage   71.02%   71.23%   +0.20%     
==========================================
  Files         142      142              
  Lines        6910     6918       +8     
==========================================
+ Hits         4908     4928      +20     
+ Misses       2002     1990      -12     

Impacted Files	Coverage Δ
src/CP/constraints/sumgreaterthan.jl	75.00% <0.00%> (-1.75%)	:arrow_down:
src/parser/constraints/sum.jl	5.73% <0.00%> (-0.20%)	:arrow_down:
src/parser/parser.jl	92.30% <50.00%> (+92.30%)	:arrow_up:
src/parser/variables.jl	73.17% <93.75%> (+7.05%)	:arrow_up:

... and 1 file with indirect coverage changes

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