fix: keep font provides styles

[farnabaz]

Do not remove style of font providers that listed in https://amp.dev/documentation/guides-and-tutorials/develop/style_and_layout/custom_fonts/

close #214

[codecov]

Codecov Report

Merging #217 (ffe7947) into master (df3b146) will increase coverage by 1.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #217      +/-   ##
==========================================
+ Coverage   66.66%   67.79%   +1.12%     
==========================================
  Files           5        5              
  Lines         171      177       +6     
  Branches       48       49       +1     
==========================================
+ Hits          114      120       +6     
  Misses         41       41              
  Partials       16       16              

Impacted Files	Coverage Δ
lib/module.js	67.85% <100.00%> (+0.38%)	⬆️
lib/utils.js	100.00% <100.00%> (ø)

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