Not choosing task

I have the following scripts setup:

``` json
"scripts": {
"start": "per-env",
"start:development": "npm run build:development",
"start:production": "npm run build:production",
"clean-styles": "rimraf web/css && mkdirp web/css",
"build": "per-env",
"build:development": "npm run styles:development",
"build:production": "npm run styles:production",
"prestyles": "per-env",
"prestyles:development": "npm run clean-styles",
"prestyles:production": "npm run clean-styles",
"styles": "per-env",
"styles:development": "node-sass src/sass/main.scss | postcss -u autoprefixer > web/css/style.css",
"styles:production": "node-sass src/sass/main.scss | postcss -u autoprefixer | cleancss > web/css/style.css"
}
```

When I run `npm start` I just get the output showing `per-env` is running and then it finishes before going to the next task.

I've tried using the example setup from the readme but I'm getting the same issue. I'm running this on Windows 10, I haven't tried on a Mac yet.