[Bug] Does not seems to support `extends` from tsconfig.json

[tebeco]

🐞 Bug report

Description

Webhint cry about missing importHelpers from tsconfig.json while it's properly setup in another tsconfig.json which is extended (and probably other similar issue)

Details

root-folder/
  |-tsconfig.json
  |-sub-folder/
    |-tsconfig.json

root-folder/tsconfig.json:

{
  "compilerOptions": {
    "importHelpers":true
  }
}

root-folder/sub-folder/tsconfig.json:

{
  "extends": "../tsconfig.json",
}

=> The compiler option "importHelpers" should be enabled to reduce the output size.Microsoft Edge Tools[typescript-config/import-helpers](https://webhint.io/docs/user-guide/hints/hint-typescript-config/import-helpers/)