fix: node 6 compatibility, take 2 (#355)

[ljharb]

Fixes #351.

[codecov]

Codecov Report

Merging #355 (91a7183) into main (edb2e01) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #355      +/-   ##
==========================================
+ Coverage   96.39%   96.42%   +0.03%     
==========================================
  Files          23       23              
  Lines         194      196       +2     
  Branches       41       42       +1     
==========================================
+ Hits          187      189       +2     
  Misses          7        7              

Impacted Files	Coverage Δ
src/parseToRgba.ts	94.73% <ø> (ø)
src/toHex.ts	100.00% <100.00%> (ø)

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[github-actions]

🎉 This PR is included in version 1.2.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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