fix: Keep `_` in patterns

[alappe]

[codecov[bot]]

Codecov Report

Merging #46 into master will increase coverage by 0.69%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #46      +/-   ##
==========================================
+ Coverage   86.01%   86.71%   +0.69%     
==========================================
  Files           1        1              
  Lines         143      143              
==========================================
+ Hits          123      124       +1     
+ Misses         20       19       -1     

Impacted Files	Coverage Δ
lib/erlex.ex	86.71% <ø> (+0.69%)	:arrow_up:

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