Allow Image Title to be centered with Image

[georgeraraujo]

Hi,
I'd like Asciidoctor EPUB to allow for the image title to be centered with the image.

I did my tests with Asciidoctor EPUB3 1.5.1 using Asciidoctor 2.0.17. I applied the workaround described in asciidoctor/asciidoctor#857 to the MWE that follows but, as described in asciidoctor/asciidoctor#857 (comment) , it only works for HTML. Here's the source code for the MWE:
mwe.zip

I ran these commands:

asciidoctor                                     mwe.adoc
asciidoctor-epub3                     -D output mwe.adoc
asciidoctor-epub3 -a ebook-format=kf8 -D output mwe.adoc

HTML output:

EPUB output viewed in Calibre 5.42.0 running on Windows:

Kindle output viewed in Kindle Paperwhite 3 (2015) 7th Gen running firmware 5.14.3: