Revert "Don't create .css.map file for minified css"
Revert "Don't create .css.map file for minified css"

This reverts commit b552c070c795342e5be7d231b9eb786620b9b323.

As discussed on Github.

xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,xs2maverick/adhocracy3.mercator