Use a more portable shebang for bash

This should increase the portability of bash scripts across various *nix
systems such as BSD-like distributions.

PR #1716 <https://github.com/Genymobile/scrcpy/pull/1716>
Signed-off-by: NLuís Ferreira <contact@lsferreira.net>
Signed-off-by: NRomain Vimont <rom@rom1v.com>

server/build_without_gradle.sh

-#!/bin/bash
+#!/usr/bin/env bash
 #
 # This script generates the scrcpy binary "manually" (without gradle).
 #