Remove the empty version line

f2678ab introduced the management of version strings by command line
attributes, but left an empty line after the authors. This seems to
upset Asciidoctor which finds an error elsewhere.

Removing the empty line seems to make it back happy.

fix progit#1134

progit.asc

@@ -1,7 +1,6 @@
 Pro Git
 =======
 Scott Chacon; Ben Straub
-
 :doctype: book
 :docinfo:
 :toc: