Allow user to run `npm repo vue-loader` and remove warn running `npm`.

According to the documentation
https://vue-loader.vuejs.org/guide/extract-css.html#webpack-3
and some private feedbacks, there are still many users use
vue-loader v15 along with webpack 3.

* [RU] Translation moved to VuePress

* custom-block.md example fix

* fix link

* options.md правка

* testing.md fix links

* linting.md fix link

* options.md added new section

* options.md add exposeFilename

* guide/README.md update

* README.md обновление

* docs: [RU] update

* pre-processors.md update

* custom-blocks.md update

fix compatibility with yarn 2

Based on good practices.

* #65 - add sassOptions for docs

fix docs with error: 'options has an unknown property 'indentedSyntax'.'
which new sass-loader are writen in 'sassOptions';
This should also cause quick prototyping's sass setting, after executing '$vue serve'

* #65 - sassOptions fix for sass-loader

* #65 - fix sassOptions - lang:ru

* add comment for sassOptions version

* add comment for sassOptions

* add comment for sassOptions

* Update docs/guide/pre-processors.md
Co-Authored-By: Haoqun Jiang <haoqunjiang@gmail.com>

* Update pre-processors.md

* Update pre-processors.md

It's a rather small change that does not affect vue-loader.
Updated to accommodate future bug fixes.

See https://github.com/vuejs/component-compiler-utils/blob/master/lib/templateCompilerModules/assetUrl.ts#L9