Can update cssnano from 3.10 to 4.0?

[genshinw]

I met this problem : cssnano/cssnano#330 ,I need to resolve it with update cssnano

[frenzzy]

Have you tried to use safe mode? #58

[NMFR]

I am waiting for a final release of cssnano v4, it seems to still be in release candidate stage.

[genshinw]

@frenzzy Thanks for help

[Hoolean]

Looks like v4 has arrived.

Also afflicted by the z-index annoyance, would be great to enjoy their upstream fix :)

[NMFR]

See #63