Block quote attribution looks misaligned

[refaelsh]

== Block quote

[quote,Monty Python and the Holy Grail]
____
Dennis: Come and see the violence inherent in the system. Help! Help! I'm being repressed!

King Arthur: Bloody peasant!

Dennis: Oh, what a giveaway! Did you hear that? Did you hear that, eh? That's what I'm on about! Did you see him repressing me? You saw him, Didn't you?
____

Here is how it looks in normal AsciiDoctor:

Please notice the attribution is properly aligned to the right.

Here is how it looks with RevealJS:

Please notice the attribution is aligned to the middle. It should be aligned to the right or left, but not the middle.
I think its a bug. Also, the fong of the attribution should be different from the quoted text, but it looks the same.