Remove flags from shebang line

Remove the `sh -ex` flags from the `test.sh` shebang line and use the
more usual form `set -ex`.

Refactor only, no logic changes.

Author: heap-coder

contrib/test.sh

@@ -1,6 +1,6 @@
-#!/bin/sh -ex
+#!/bin/sh
 
-set -e
+set -ex
 
 FEATURES="compiler serde rand"