t7501-commit.sh: Not all seds understand option -i

Use mv instead.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7501-commit.sh

@@ -79,7 +79,8 @@ test_expect_success \
 
 cat >editor <<\EOF
 #!/bin/sh
-sed -i -e "s/a file/an amend commit/g" $1
+sed -e "s/a file/an amend commit/g" < $1 > $1-
+mv $1- $1
 EOF
 chmod 755 editor
 
@@ -98,7 +99,8 @@ test_expect_success \
 
 cat >editor <<\EOF
 #!/bin/sh
-sed -i -e "s/amend/older/g" $1
+sed -e "s/amend/older/g"  < $1 > $1-
+mv $1- $1
 EOF
 chmod 755 editor