Fix accessing outer directories in tsconfig

[LukeAbby]

With a tsconfig like this I noticed that arktype was puking:

{
  "extends": "../tsconfig.base.json",
  "compilerOptions": {
    "typeRoots": "../node_modules/@types",
    "types": ["node"] // Doesn't matter what.
  }
}

Specifically when the directory of the config was, say, tests it'd try tests/tsconfig.base.json instead of tsconfig.base.json. This ended up being because arktype gave a relative path and so ./../tsconfig.base.json simplified to ./tsconfig.base.json and . was tests.

[ssalbdivad]

Great, thanks!