Fix webpack dev mode warnings

Switched to [@gravity-ui/app-builder](https://github.com/gravity-ui/app-builder) as build library in my project and got this warnings in dev mode:

```
WARNING in ./node_modules/@doc-tools/transform/dist/css/yfm.css (./node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[3].use[1]!./node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[3].use[2]!./node_modules/resolve-url-loader/index.js??ruleSet[1].rules[1].oneOf[3].use[3]!./node_modules/@doc-tools/transform/dist/css/yfm.css)
Module Warning (from ./node_modules/resolve-url-loader/index.js):
resolve-url-loader: webpack misconfiguration
webpack or the upstream loader did not supply a source-map
```