Passing additional args breaks scripts

`package.json`:

``` js
{
"test": "per-env",
"test:development": "mocha --watch",
"test:test": "mocha"
}
```

Breaks:

``` shell
$ npm test -- --grep api

> @terse/webpack@0.0.5 test /Users/Eric/Projects/ericclemmons/terse-webpack
> per-env "--grep" "api"

> @terse/webpack@0.0.5 test:development /Users/Eric/Projects/ericclemmons/terse-webpack
> mocha --watch "api"

/Users/Eric/Projects/ericclemmons/terse-webpack/node_modules/mocha/lib/utils.js:634
throw new Error("cannot resolve path (or pattern) '" + path + "'");
^

Error: cannot resolve path (or pattern) 'api'
```

Works:

``` shell
$ npm run test:development -- --grep api
```