zat package removes mask property when compressing SVGs

[kibin]

When I run zat package, all my SVG-icons look broken.
When I start to investigate what’s going on I see that all the mask properties has been stripped from the resulting file.

Before (see next-to-last string, path tag):

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <defs/>
  <defs>
    <mask id="b">
      <radialGradient id="a">
        <stop offset="0" stop-color="#fff"/>
        <stop offset="1"/>
      </radialGradient>
      <text y="50" fill="url(#a)" font-family="Arial" font-size="20">
        SVG Mask
      </text>
    </mask>
  </defs>
  <path fill="#B63FC4" d="M0 0h100v100H0z" mask="url(#b)"/>
</svg>

After (with all the white spaces returned):

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <defs/>
  <defs>
    <mask id="b">
      <radialGradient id="a">
        <stop offset="0" stop-color="#fff"/>
        <stop offset="1"/>
      </radialGradient>
      <text y="50" fill="url(#a)" font-family="Arial" font-size="20">
        SVG Mask 
      </text>
    </mask>
  </defs>
  <path fill="#B63FC4" d="M0 0h100v100H0z"/>
</svg>

You can see that the last <path> tag has no mask property, which breaks SVG and turns it into a simple rectangle instead of text with a mask.
Also it’s strange that this operation (compressing) is destructive on the source (it’s affecting svgs in zat/assets).