completion: mark bash script as LF-only

Without this change, the completion script does not work, as Bash expects its scripts to have line feeds as end-of-line markers (this is particularly prominent in quoted multi-line strings, where carriage returns would slip into the strings as verbatim characters otherwise). This change is required to let t9902-completion pass when Git's source code is checked out with `core.autocrlf = true`. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>