t4029: use sh instead of bash

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4029-diff-trailing-space.sh

diff --git a/t/t4029-diff-trailing-space.sh b/t/t4029-diff-trailing-space.sh
index 9ddbbcd..3ccc237 100755
--- a/t/t4029-diff-trailing-space.sh
+++ b/t/t4029-diff-trailing-space.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 #
 # Copyright (c) Jim Meyering
 #