docs: fix typo fontEmbedCss -> fontEmbedCSS

[leadream]

Description

Change fontEmbedCss to fontEmbedCSS in the doc because the option name is fontEmbedCSS.

[vivcat[bot]]

👋 @leadream

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b751cbf) 62.93% compared to head (2833c87) 62.93%. Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #441 +/- ## ======================================= Coverage 62.93% 62.93% ======================================= Files 10 10 Lines 580 580 Branches 143 143 ======================================= Hits 365 365 Misses 151 151 Partials 64 64 ```

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