Fixed NormalVector for simplices

[fverdugo]

This addresses issue #97

[codecov-io]

Codecov Report

Merging #98 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master     #98   +/-   ##
======================================
  Coverage    92.4%   92.4%           
======================================
  Files          85      85           
  Lines        4397    4397           
======================================
  Hits         4063    4063           
  Misses        334     334

Impacted Files	Coverage Δ
src/Integration/NormalVectors.jl	88% <100%> (ø)	⬆️

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