Fix flash for sudo

When executed under sudo the wrong shell is used by Debian, causing an
error. This patch fixes the script so it specifies which shell to use.

Note that you don't need to run flash.sh under sudo because it sudos
itself.

flash.sh

@@ -1,3 +1,4 @@
+#!/bin/bash
 set -o pipefail
 if ! command -v openocd &> /dev/null
 then

flash_experimental.sh

@@ -1,3 +1,4 @@
+#!/bin/bash
 set -o pipefail
 if ! command -v openocd &> /dev/null
 then