v1.9.x fails to build or run dev on a default project

[xvdd]

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

Bug report

With v1.9, an error with shared-utils env.js prevents to run a default VuePress project.

Steps to reproduce

Create boilerplate VuePress site using the Getting Started guide:

$ yarnpkg create vuepress-site test
$ cd test/docs
$ yarnpkg install
$ yarnpkg dev

What is expected?

Running the dev server on port 8080

What is actually happening?

$ yarnpkg dev
yarn run v1.22.4
$ vuepress dev src
/home/<dir>/test/docs/node_modules/@vuepress/shared-utils/lib/env.js:3
    isDebug;
           ^

SyntaxError: Unexpected token ;
    at Module._compile (internal/modules/cjs/loader.js:723:23)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Module.require (internal/modules/cjs/loader.js:692:17)
    at require (internal/modules/cjs/helpers.js:25:18)
    at Object.<anonymous> (/home/<dir>/test/docs/node_modules/@vuepress/shared-utils/lib/index.js:38:31)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Other relevant information

• Output of npx vuepress info in my VuePress project:

$ npx vuepress info
Unexpected token ;

• Ubuntu 20.04.3 LTS (Focal Fossa)
• Node: 10.19.0
• yarnpkg: 1.22.4
• npm: 6.14.4
• vuepress: 1.9.5

Affected Versions

Forcing vuepress to v1.8.2 in package.json runs and builds successfully.

Affected versions tested KO:

• v1.9.5
• v1.9.4
• v1.9.2
• v1.9.0

Test with npm

npm run dev fails with the same error after npm install on the default project.

[patchshorts]

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