t/t9902-completion.sh: backslashes in echo

The usage of backslashes in echo is not portable.  Since some tests
tries to output strings containing '\b' it is safer to use printf
here.  The usage of printf instead of echo is also preferred by POSIX.

Signed-off-by: Marcel Telka <marcel@telka.sk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9902-completion.sh

@@ -73,7 +73,7 @@ _get_comp_words_by_ref ()
 print_comp ()
 {
 	local IFS=$'\n'
-	echo "${COMPREPLY[*]}" > out
+	printf '%s\n' "${COMPREPLY[*]}" > out
 }
 
 run_completion ()