FIXMEs in AsciidocLanguageBlockElementsTest

Modification of the Asciidoc-Wikitext implementation to fix the FIXMEs in AsciidocLanguageBlockElementsTest.

FIXMEs were introduced with Pull Request #2

Same rule applies to the tests from the test suite: they need to pass with both the Asciidoc-Wikitext and the Asciidoctor implementations.