Pin stylus dependency

Hi,

From today I've been experiencing some errors returning from the `component-build` process like the following:

```
[TypeError: /Users/cristian/Work/my-app/lib/header/header.styl:104
   100|         padding-right: 0;
   101|         margin-left: 5px;
   102|         margin-right: 5px;
   103|         display: block;
 > 104| 

Arguments to path.resolve must be strings
]
```

There was no extra description on the error, but I started digging from here and I found that since `stylus@0.44.0` release (a day ago) all my applications fell in pieces.

I also found that by pinning `stylus` to `0.43.1`, this error vanishes.

I could debug this a little more to get a more clear resolution on why `stylus` breaks, but for now...

:dancers: 

I'd be glad if this could be merged asap. I'm now using the fork I did (so, no rush). But I'd rather use the npm version of this.