CLI: Replace path.join with path.resolve

This fixes an issue where absolute paths couldn't be used with the -t option.

`path.resolve` is a lot cleverer than `path.join` (which is rather naive). For example:

```js
path.join('foo', '/bar')    // -> 'foo/bar'
path.resolve('foo', '/bar') // -> '/bar'
```

`path.resolve` also defaults to using the current working directory if no `from` argument is supplied, so we can leave that out.