add INIT_CWD environment variable

[crusty-voidzero]

Imported from voidzero-dev/vite-plus#74

Scripts are run from the root of the package folder, regardless of what the current working directory is when npm is invoked. If you want your script to use different behavior based on what subdirectory you're in, you can use the INIT_CWD environment variable, which holds the full path you were in when you ran npm run.

https://docs.npmjs.com/cli/v8/using-npm/scripts