Fix for !global for the latest update

Patch for the following warning in Sass 3.3_rc4.

```
Assigning to global variable "$modules" by default is deprecated.
In future versions of Sass, this will create a new local variable.
If you want to assign to the global variable, use "$modules: () !global !default" instead.
```
Merge pull request #9 from xzyfer/patch-2

Fix for !global for the latest update