t4013 diff format tests update

This changes one test commit in the sequence to have more than
one lines of commit log.  A few output formats (--pretty=email
aka format-patch and --pretty=oneline) need to behave
differently on single and multi-line log, and this change will
help catching breakages.

Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t4013/diff.diff-tree_-c_--stat_master

@@ -1,5 +1,5 @@
 $ git diff-tree -c --stat master
-176b998f5d647cbd77a9d8acf4531e930754d16d
+59d314ad6f356dd08601a4cd5e530381da3e3c64
  dir/sub |    2 ++
  file0   |    3 +++
  2 files changed, 5 insertions(+), 0 deletions(-)