Update bitset package import path

[zhsj]

Upstream has renamed their repo path.

[codecov]

Codecov Report

Merging #163 (abf9dd9) into master (a2552c5) will not change coverage.
The diff coverage is n/a.

❗ Current head abf9dd9 differs from pull request most recent head 1def3a9. Consider uploading reports for the commit 1def3a9 to get more accurate results

@@           Coverage Diff           @@
##           master     #163   +/-   ##
=======================================
  Coverage   44.27%   44.27%           
=======================================
  Files          16       16           
  Lines         804      804           
=======================================
  Hits          356      356           
  Misses        401      401           
  Partials       47       47           

Flag	Coverage Δ
integtests	∅ <ø> (?)
unittests	44.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
plugins/allocators/bitmap/bitmap.go	70.58% <ø> (ø)
plugins/allocators/bitmap/bitmap_ipv4.go	77.27% <ø> (ø)
plugins/prefix/plugin.go	48.48% <ø> (ø)

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[Natolumin]

done in #169