Skip coverage unless on Linux with Julia 1.2

[abelsiqueira]

No description provided.

[coveralls]

Coverage increased (+0.5%) to 92.543% when pulling d751504 on abelsiqueira:coverage into 356c49c on JuliaSmoothOptimizers:master.

[codecov]

Codecov Report

Merging #116 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #116      +/-   ##
==========================================
- Coverage   92.59%   92.54%   -0.06%     
==========================================
  Files           6        6              
  Lines         527      523       -4     
==========================================
- Hits          488      484       -4     
  Misses         39       39

Impacted Files	Coverage Δ
src/PreallocatedLinearOperators.jl	77.27% <0%> (-1.46%)	⬇️
src/LinearOperators.jl	94.04% <0%> (-0.03%)	⬇️

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