.vuepress/config.ts does not respect custom command

[ulivz]

• I confirm that this is an issue rather than a question.

Bug report

Steps to reproduce

1. Using .vuepress/config.ts introduced at v1.9.0
2. Try to use https://github.com/ulivz/vuepress-plugin-check-md but it does not work

What is expected?

VuePress should load plugins defined in config.ts correctly.

What is actually happening?

VuePress should load plugins defined in config.ts.

Other relevant information

• Output of npx vuepress info in my VuePress project:

Environment Info:

  System:
    OS: macOS 12.3
    CPU: (10) arm64 Apple M1 Max
  Binaries:
    Node: 16.18.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 8.19.2 - /usr/local/bin/npm
  Browsers:
    Chrome: 108.0.5359.124
    Edge: Not Found
    Firefox: Not Found
    Safari: 15.4
  npmPackages:
    @vuepress/core: Not Found
    @vuepress/theme-default: Not Found
    vuepress: 1.9.5 => 1.9.5
  npmGlobalPackages:
    vuepress: Not Found