bash is not available everywhere. Use #!/usr/bin/env sh instead

which should work on most posix platforms. Fixes OpenBSD.

Signed-off-by: Tobias Heider <me@tobhe.de>

data/makelogo.sh

@@ -1,3 +1,3 @@
-#!/bin/bash
+#!/usr/bin/env sh
 convert bootlogo_128.png -background black -flatten -depth 8 rgba:bootlogo_128.bin
 convert bootlogo_256.png -background black -flatten -depth 8 rgba:bootlogo_256.bin