feat!: default to font-display: swap unless preloading

[kara]

This commit sets the font-display default to 'swap',
unless the preload option is set to true. Either way,
the font-display value is still user-overridable using
the display option.

We generally recommend using 'swap' because it's the
best way to avoid FOIT (flash of invisible text) and
optimize LCP while still guaranteeing the web font
will load (unlike optonal).

[codecov]

Codecov Report

Merging #88 (fa4d4e0) into master (fa4d4e0) will not change coverage.
The diff coverage is n/a.

❗ Current head fa4d4e0 differs from pull request most recent head 37358de. Consider uploading reports for the commit 37358de to get more accurate results

@@            Coverage Diff            @@
##            master       #88   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines           43        43           
  Branches        13        13           
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  Hits            43        43           

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[ricardogobbosouza]

Thanks @kara