if you have svgs with unquoted attributes such as:
xmlns="http://www.w3.org/2000/svg" width=20px height=20px

The error: Error in parsing SVG: Unquoted attribute value is emitted.

I've created a loader to temporary fix this:
https://www.npmjs.com/package/xml-fix-loader

{
  test: /\.svg$/,
  use: [
    { loader: 'file-loader' },
    { loader: 'xml-fix-loader' }
  ]
}
...
plugins: [
  ...
  new ImageminPlugin()
]

Also opened a bug on svgo:
svg/svgo#678