feat: support vuepress2 rc12

[coveralls]

Pull Request Test Coverage Report for Build 9249335748

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.5%) to 56.369%

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Files with Coverage Reduction	New Missed Lines	%
tools/helper/src/node/page/excerpt.ts	5	83.1%
<!--	Total:	5		-->

Totals
Change from base Build 9219657180:	-0.5%
Covered Lines:	988
Relevant Lines:	1567

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💛 - Coveralls