Rename `spec._class` to `spec.__class`
Rename `spec._class` to `spec.__class`

Prefix overridable attributes such as `class` with a `__` to distinguish it as a should-not-modify property.
markbrouch/generator-yeogurt,OnkelTem/generator-yeogurt,markbrouch/generator-yeogurt,larsonjj/generator-yeogurt,larsonjj/generator-yeogurt,OnkelTem/generator-yeogurt