fix: cssnano types

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fixes #146

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #147 (0ae24ad) into master (b5b0cbc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #147   +/-   ##
=======================================
  Coverage   95.86%   95.86%           
=======================================
  Files           3        3           
  Lines         266      266           
  Branches      107      107           
=======================================
  Hits          255      255           
  Misses         11       11           

Impacted Files	Coverage Δ
src/index.js	98.09% <ø> (ø)
src/utils.js	91.66% <ø> (ø)

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