resolves #1324 use middle instead of center in vertical-align example [skip ci]
resolves #1324 use middle instead of center in vertical-align example [skip ci]

asciidoctor/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,Hextremist/asciidoctor-pdf,Hextremist/asciidoctor-pdf,dsisnero/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,dsisnero/asciidoctor-pdf