SVG Pattern in SVG supported by react-sketchapp ?
**Proposal/Feature-request:**

Like this. 

```svg

<svg width="140" height="140">
  <defs>
   <pattern id="toto" patternUnits="userSpaceOnUse" width="20" height="20">
     <path d="M 0,20 l 20,-20 M -5,5 l 10,-10 M 15,25 l 10,-10" stroke-width="2" shape-rendering="auto" stroke="#343434" stroke-linecap="square">
     </path>
   </pattern>
  </defs>
  <path d="M 0 0 L 0 140 L 140 140 L 140 0 Z" fill="url(#toto)"></path>
</svg>

```

To get this:

<img width="163" alt="pattern" src="https://user-images.githubusercontent.com/197471/36358446-7d8be6c6-14dc-11e8-8ce9-edde078954c4.png">



