chore: remove refs to deprecated io/ioutil

[testwill]

No description provided.

[codecov-commenter]

Codecov Report

Merging #423 (80424cf) into master (1a4b844) will not change coverage.
Report is 4 commits behind head on master.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##           master     #423   +/-   ##
=======================================
  Coverage   94.96%   94.96%           
=======================================
  Files           3        3           
  Lines         159      159           
=======================================
  Hits          151      151           
  Misses          6        6           
  Partials        2        2           

Files Changed	Coverage Δ
mimetype.go	94.82% <100.00%> (ø)

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