fix: data URI for image/svg+xml

[alexander-akait]

What kind of change does this PR introduce?

bugfix webpack-contrib/css-loader#1342

Did you add tests for your changes?

yes

Does this PR introduce a breaking change?

no

What needs to be documented once your changes are merged?

nothing

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[alexander-akait]

Good idea, we have couple bugs in our regexp, but I will fix them late, I think better to have simple parser on this

[sokra]

Thanks