ng generate library virtusUI --style=scss gives an error

```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```
It would be cool to generate library with SCSS system.
```
ng generate library virtusUI --style=scss
```
Now I'm getting an error
```
Schematic input does not validate against the Schema: {"style":"scss","entryFile":"public_api","prefix":"lib","skipPackageJson":false,"skipTsConfig":false}
Errors:

Data path "" should NOT have additional properties(style).
```

首先重現 `ng generate library virtusUI --style=scss`，並檢查程式庫產生 schematic 及其 schema 驗證。當 `style` 選項被接受，且產生的程式庫使用 SCSS 而不出現 additional-properties 錯誤時，此變更即完成。

由索引模型根據 Issue 內容生成。