make t8001 work on Mac OS X again

make t8001 work on Mac OS X again

The test was recently broken to expect sed to leave the
incomplete line at the end without newline.

POSIX says that output of the pattern space is to be followed by
a newline, while GNU adds the newline back only when it was
stripped when input.  GNU behaviour is arguably more intuitive
and nicer, but we should not depend on it.

Signed-off-by: Johannes Schindelin <redacted>
Acked-by: Shawn O. Pearce <redacted>
Signed-off-by: Junio C Hamano <redacted>