Change bash scripts to be POSIX-compatible

some Unix-like operating systems, namely Alpine, don't come with bash
preinstalled.
scripts in the lib-src/ directory were left untouched.

Signed-off-by: Sol Fisher Romanoff <sol@solfisher.com>

linux/build-environment/entrypoint.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 conan --version