feat: fallback to async API on processSync error via synckit

[JounQin]

close #203

https://github.com/rx-ts/synckit

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[codecov-commenter]

Codecov Report

Merging #307 (2d532f1) into master (a893aa7) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #307   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines          451       468   +17     
  Branches        90        96    +6     
=========================================
+ Hits           451       468   +17     

Impacted Files	Coverage Δ
packages/eslint-plugin-mdx/src/rules/helpers.ts	100.00% <100.00%> (ø)
packages/eslint-plugin-mdx/src/rules/remark.ts	100.00% <100.00%> (ø)

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[JounQin]

Thanks to @codesandbox, I found a bug locally, and it's just working now!