…fig/tasks.js

Renamed `settings.prefix.browsers` to `overrideBrowserslist` to get rid of the following warning when building:

```
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
```