mono color inverted menu

Why not to keep the `box-shadow` on inverted color menus? It looks more consistent on dark backgrounds, may be keep both options by adding a new `.mono` variation: 

```CSS
.ui.inverted.mono.menu .active.item {
  box-shadow: none !important;
}
.ui.inverted.menu .active.item {
  /*box-shadow: none !important;*/
  background-color: rgba(255, 255, 255, 0.2);
}
```

>Normal 
![inverted color](https://f.cloud.github.com/assets/4712046/2240111/cc90b2bc-9c75-11e3-87ab-1663fddac23b.png)

>Mono
![mono](https://f.cloud.github.com/assets/4712046/2240106/a6a82e18-9c75-11e3-852e-b37ee92e280e.png)