Bug with bibliography example in documentation

Fix documentation about bibliography

As pointed by matt at: https://groups.google.com/forum/?fromgroups=#!topic/asciidoc/Toebf1FFYd0

I tested and it's there:

$ cat bibtest.txt 
== Text

Some text.

[bibliography]
.Optional list title
- [[[taoup]]] Eric Steven Raymond. 'The Art of UNIX
  Programming'. Addison-Wesley. ISBN 0-13-142901-9.
- [[[walsh-muellner]]] Norman Walsh & Leonard Muellner.
  'DocBook - The Definitive Guide'. O'Reilly & Associates.
  1999. ISBN 1-56592-580-7.

$ asciidoc bibtest.txt 
asciidoc: WARNING: bibtest.txt: line 11: list item index: expected 1 got 1999