fix: incorrect default ecmaVersion (2022 is unavailable yet)

[JounQin]

close #366

[codesandbox-ci]

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[JounQin]

@wooorm Back port known issues for legacy projects.

[codecov-commenter]

Codecov Report

Merging #402 (40d0785) into release-v1 (16c5934) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           release-v1      #402   +/-   ##
============================================
  Coverage      100.00%   100.00%           
============================================
  Files              21        21           
  Lines             519       519           
  Branches          111       111           
============================================
  Hits              519       519           

Impacted Files	Coverage Δ
packages/eslint-mdx/src/parser.ts	100.00% <ø> (ø)

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[JounQin]

Ready for a release from release-v1 branch.