treat SCSS @else as a template_else token type

```
@mixin block-size( $size: $global-block-context, $context: $global-block-context ) {
  @if $size == $context {
    width: 100%;
  }
  @else {
    width: percentage($size / $context);
  }
}
```

The `@else` line should be `} @else {`