Make sure moduleName does not include cwd.

Maybe I am being a bit stupid (I hope not), but I had to make this change to get correct AMD modules names. For example if you change the `module` options to `amd` and compile the fixture files you get something like:

```js
define("test_fixtures/args", [], function() {
  // module here
});
```

Notice the inclusion of `text_fixtures/` in the module name. With this change it now outputs:

```js
define("args", [], function() {
  // module here
});
```