`image-rendering` property causes Class Cast Exception.

[jeeeyul]

Steps to Reproduce

1. Prepare a simple css file that contains:

   .foo {
   	image-rendering: pixelated;
   }
   

2. Validate it with Unicorn.

Expected Behavior

1. Validation should have to be passed.

Actual Result

1. An Unknown Error was raised that caused by Class Cast Exception.

알 수 없는 오류 java.lang.Exception: class org.w3c.css.properties.css3.Css3Style cannot be cast to class org.w3c.css.properties.svg.SVGBasicStyle (org.w3c.css.properties.css3.Css3Style and org.w3c.css.properties.svg.SVGBasicStyle are in unnamed module of loader org.w3c.jigsaw.servlet.AutoReloadServletLoader @4cd2c9a1)

References

• https://w3c.github.io/csswg-drafts/css-images/#the-image-rendering