Revert "Update doc/Jamfile"

This reverts commit 9899acb.

Author: pdimov

doc/Jamfile

@@ -2,7 +2,7 @@
 # Distributed under the Boost Software License, Version 1.0.
 # https://www.boost.org/LICENSE_1_0.txt
 
-using asciidoctor ;
+import asciidoctor ;
 
 html describe.html : describe.adoc ;