all: remove use of deprecated io/ioutil package

[sbinet]

No description provided.

[codecov]

Codecov Report

Merging #173 (c398aac) into master (d6a3924) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   72.90%   72.90%           
=======================================
  Files          71       71           
  Lines       11683    11683           
=======================================
  Hits         8517     8517           
  Misses       2595     2595           
  Partials      571      571           

Impacted Files	Coverage Δ
modules/runtime.go	54.88% <100.00%> (ø)
py/file.go	58.77% <100.00%> (ø)
pytest/pytest.go	49.09% <100.00%> (ø)

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