t9301: use ISO8859-1 rather than ISO-8859-1

Some ancient platforms do not have an extensive list of alternate names for
character encodings.  For example, Solaris 7 does not know that ISO-8859-1
is the same as ISO8859-1.  Modern platforms do know this, so use the older
name.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9301-fast-export.sh

@@ -68,7 +68,7 @@ test_expect_success 'fast-export master~2..master' '
 
 test_expect_success 'iso-8859-1' '
 
-	git config i18n.commitencoding ISO-8859-1 &&
+	git config i18n.commitencoding ISO8859-1 &&
 	# use author and committer name in ISO-8859-1 to match it.
 	. "$TEST_DIRECTORY"/t3901-8859-1.txt &&
 	test_tick &&