shell doc: remove stray "+" in example

The git-shell(1) manpage says EXAMPLE To disable interactive logins, displaying a greeting instead: + $ chsh -s /usr/bin/git-shell $ mkdir $HOME/git-shell-commands [...] The stray "+" has been there ever since the example was added in v1.8.3-rc0~210^2 (shell: new no-interactive-login command to print a custom message, 2013-03-09). The "+" sign between paragraphs is needed in asciidoc to attach extra paragraphs to a list item but here it is not needed and ends up rendered as a literal "+". Remove it. A quick search with "grep -e '<p>+' /usr/share/doc/git/html/*.html" doesn't find any other instances of this problem. Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>