add test to verify vertical alignment of AsciiDoc table cell is honored
add test to verify vertical alignment of AsciiDoc table cell is honored

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