fix bsd shell negation

diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index cb860296edfab2d117fc8b62505df00a51baed02..8fc39d77cec6168dae930beef785597dace24aa3 100755 (executable)
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -5,7 +5,9 @@ test_description='blob conversion via gitattributes'
 . ./test-lib.sh
 
 cat <<\EOF >rot13.sh
-tr '[a-zA-Z]' '[n-za-mN-ZA-M]'
+tr \
+  'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' \
+  'nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM'
 EOF
 chmod +x rot13.sh