scripts: make shebang more portable (#2216)

Some Linux distros (like NixOS) don't place bash in /bin/bash.

scripts/copyfile.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright (c) 2018-2019 Status Research & Development GmbH. Licensed under
 # either of:

scripts/make_prometheus_config.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright (c) 2020 Status Research & Development GmbH. Licensed under
 # either of:

scripts/makedir.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright (c) 2018-2020 Status Research & Development GmbH. Licensed under
 # either of:

wasm/build.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Simple build script to produce an Emscripten-based wasm version of the state
 # sim.

wasm/build_ncli.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Simple build script to produce an Emscripten-based wasm version of the state
 # sim.