Support "pure" scope in postcss-modules-local-by-default

[StarpTech]

I'd like to use pure scope in css-modules/postcss-modules-local-by-default

https://github.com/css-modules/postcss-modules-local-by-default/blob/master/index.js#L527-L534

[cloud031998]

#237