doc: fix list continuation in alias.adoc

Add missing list continuation marks ('+') after code blocks and shell examples
so paragraphs render correctly as part of the preceding list item.

Signed-off-by: Jonatan Holmgren <jonatan@jontes.page>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/alias.adoc

@@ -36,7 +36,7 @@ With a Git alias defined, e.g.,
     $ git config --global alias.last.command "cat-file commit HEAD"
 +
 `git last` is equivalent to `git cat-file commit HEAD`.
-
++
 To avoid confusion and troubles with script usage, aliases that
 hide existing Git commands are ignored except for deprecated
 commands.  Arguments are split by