Update library version to 3.8.1

[Enkidu93]

Needed for sillsdev/serval#886

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This change is 

[ddaspit]

@ddaspit reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on Enkidu93).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.79%. Comparing base (4db48d7) to head (40a0126).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #394   +/-   ##
=======================================
  Coverage   72.79%   72.79%           
=======================================
  Files         424      424           
  Lines       36309    36309           
  Branches     5006     5006           
=======================================
  Hits        26431    26431           
  Misses       8770     8770           
  Partials     1108     1108           

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