t4301: emit blank line in more idiomatic fashion

t4301: emit blank line in more idiomatic fashion

The unusual use of:

    printf "\\n" >>file &&

may give readers pause, making them wonder why this form was chosen over
the more typical:

    printf "\n" >>file &&

However, even that may give pause since it is a somewhat unusual and
long-winded way of saying:

    echo >>file &&

Therefore, replace `printf` with the more idiomatic `echo`, with the
hope of eliminating a possible stumbling block for those reading the
code.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>