Merge branch 'shebang' into 'main'

Update shebang in scripts to improve portability

See merge request systemrescue/systemrescue-sources!313

build.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e -u
 

docker/build-docker-image.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Parameters validation
 if [ -z "${sysrescuearch}" ] ; then

docker/build-iso-image.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Parameters validation
 if [ -z "${sysrescuearch}" ] ; then