Workaround for failure to update version.h due to git branch name

[akohlmey]

Git branch names may contain the '/' character (the github CLI does this when checking out pull requests that have a branch name that clashes with a branch in the current repo) which breaks the sed command to update version.h and thus compilation fails. This PR substitutes all '/' characters with '_' in the git branch name and thus works around that issue.

[codecov-commenter]

Codecov Report

Merging #3 (7b926e1) into master (ad8e1ea) will decrease coverage by 0.04%.
The diff coverage is 41.17%.

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
- Coverage   72.27%   72.22%   -0.05%     
==========================================
  Files         130      130              
  Lines       14234    14249      +15     
==========================================
+ Hits        10287    10292       +5     
- Misses       3947     3957      +10     

Flag	Coverage Δ
cpp	75.00% <41.17%> (-0.05%)	⬇️
python	72.22% <41.17%> (-0.05%)	⬇️

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Impacted Files	Coverage Δ
src/libnnptrain/Training.cpp	73.20% <37.50%> (-0.37%)	⬇️
src/libnnp/Settings.cpp	94.19% <100.00%> (+0.02%)	⬆️

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