postcss-minify-selectors 
Minify selectors with PostCSS.
Install
With npm do:
npm install postcss-minify-selectors --save
Example
Input
h1 + p, h2, h3, h2{color:blue}
Output
h1+p,h2,h3{color:blue}
For more examples see the tests.
Usage
See the PostCSS documentation for examples for your environment.
Contributing
Pull requests are welcome. If you add functionality, then please add unit tests to cover it.
License
MIT