moving shebang at the top of the file

Shebang changes how Unix-like OS run scripts, ensuring the script is run with the specified interpreter. In this case as the line was not the first in the file, users without bash as their default shell would experience issues running the script.

Fixes arduino#9281
More details on shebang usage here https://en.wikipedia.org/wiki/Shebang_(Unix)

build/linux/dist/arduino-linux-setup.sh

@@ -1,3 +1,4 @@
+#!/bin/bash
 # arduino-linux-setup.sh : A simple Arduino setup script for Linux systems
 # Copyright (C) 2015 Arduino Srl
 #
@@ -61,8 +62,6 @@
 #	+ now the script checks for SUDO permissions
 #
 
-#!/bin/bash
-
 # if [[ $EUID != 0 ]] ; then
 #   echo This must be run as root!
 #   exit 1