Support render svg

[Zipexpo]

For who has an issue with svg using this library:
I have trouble with render target have svg (d3js created). So, I update aframe-html-shader with newest html2canvas and have some "trick" to make the svg show:

• svg must have the size (in css)
• must add data-html2canvas-ignore="true" into a-scence tag

https://github.com/Zipexpo/aframe-html-shader