Documentation: remove stray backslash from "git bundle" manual

Documentation: remove stray backslash from "git bundle" manual

In v1.6.2.2~6^2~4 (Documentation: minor grammatical fixes
and rewording in git-bundle.txt, 2009-03-22), backslashes were
introduced before ~ to avoid introducing unintentional
superscripts.  In one paragraph there is only one ~, though,
making that not a candidate for quoting, and asciidoc 8.5.8
passes the backslash through so the man page says "\~10..master".

Maybe there is an asciidoc behavior change involved.

In any case, we should replace tildes with a {tilde} entity which
means the same thing regardless of where it is found.

Reported-by: Frédéric Brière <fbriere@fbriere.net>
Cc: David J. Mellor <dmellor@whistlingcat.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>