Replace Autoprefixer `browsers` option to Browserslist config.

[mobihack]

Replace Autoprefixer browsers option to Browserslist config.

 Use `browserslist` key in `package.json` or `.browserslistrc` file.

 Using `browsers` option cause some error. Browserslist config 
 can be used for Babel, Autoprefixer, postcss-normalize and other tools.

 If you really need to use option, rename it to `overrideBrowserslist`.

 Learn more at:
 https://github.com/browserslist/browserslist#readme
 https://twitter.com/browserslist