loader: add remark-loader to the list

[anshumanv]

Closes #3900

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[EugeneHlushko]

https://github.com/webpack/webpack.js.org/blob/master/repositories/loaders.json add the loader here and see if its added to the main list

[alexander-akait]

Somebody can create an issue, postcss/postcss-loader is now here https://github.com/webpack-contrib/postcss-loader

[anshumanv]

will do

[anshumanv]

Fixed here - #3909

[EugeneHlushko]

Thanks!