mingw: fix the shortlog --output=<file> test

Adjust t4201 to pass on Windows; a couple of test cases need to be
skipped on Windows which leads to a different shortlog than on Linux.

Let's just fix that by limiting the shortlog's commit range to traverse
only one commit: that guarantees that it does not matter how many test
cases were skipped.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4201-shortlog.sh

@@ -185,9 +185,9 @@ test_expect_success 'shortlog with revision pseudo options' '
 '
 
 test_expect_success 'shortlog with --output=<file>' '
-	git shortlog --output=shortlog master >output &&
+	git shortlog --output=shortlog -1 master >output &&
 	test ! -s output &&
-	test_line_count = 7 shortlog
+	test_line_count = 3 shortlog
 '
 
 test_done