t5520: let sed open its own input

We were using a redirection operator to feed input into sed. However,
since sed is capable of opening its own files, make sed open its own
files instead of redirecting input into it.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5520-pull.sh

@@ -5,7 +5,7 @@ test_description='pulling into void'
 . ./test-lib.sh
 
 modify () {
-	sed -e "$1" <"$2" >"$2.x" &&
+	sed -e "$1" "$2" >"$2.x" &&
 	mv "$2.x" "$2"
 }