Use env in shebangs.

compile-tun2sock.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Compiles tun2socks for Linux.
 # Intended as a convenience if you don't want to deal with CMake.

compile-udpgw.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Compiles udpgw for Linux.
 # Intended as a convenience if you don't want to deal with CMake.

ncd/parse_linux_input.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 INPUT=$1
 OUTPUT=$2