modified private method indentation for better readability

In most languages I've worked in the private marker is not generally the same indentation as the methods it encapsulates. I've adopted this over many years, and would like to keep it if we can, as I find it very useful for scanning classes.


```ruby
class MyClass

  def public_method
    # ...
  end

  private

    def private_method
      # ..
    end

end
```