Try using sh instead of bash

scripts/build_test.sh

@@ -1 +0,0 @@
-echo 1

scripts/build_upstream.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 export CUSTOM_TAG="v$OPENVPN_VERSION"
 export BUILD_ARGS="--build-arg OPENVPN_VERSION=$OPENVPN_VERSION"
 build-container

scripts/build_xor.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 git clone https://github.com/Tunnelblick/Tunnelblick.git /tmp/tunnelblick
 export OPENVPN_VERSION=$(ls /tmp/tunnelblick/third_party/sources/openvpn | sed 's/openvpn-//g' | sort  -k1,1nr -k2,2n -k3,3n | head -n 1)
 export CUSTOM_TAG="v$OPENVPN_VERSION-XOR-$TUNNELBLICK_VERSION"