Update prepare script

scripts/prepare

-#!/bin/bash
+#!/bin/sh
 
 PROJDIR="$(cd "$(dirname "${0}")/../" && pwd)"
 
-if [[ ! -d "${PROJDIR}/lib/qtil" ]]; then
+if [ ! -d "${PROJDIR}/lib/qtil" ]; then
     git clone https://github.com/akiraohgaki/qtil.git -b release-0.4.0 --single-branch --depth=1 "${PROJDIR}/lib/qtil"
 fi
 
-if [[ ! -d "${PROJDIR}/lib/AppImageUpdate" ]]; then
+if [ ! -d "${PROJDIR}/lib/AppImageUpdate" ]; then
     git clone https://github.com/AppImage/AppImageUpdate.git -b continuous --single-branch --depth=1 "${PROJDIR}/lib/AppImageUpdate"
     git -C "${PROJDIR}/lib/AppImageUpdate" submodule update --init --recursive #--depth=1
 fi
 
-if [[ ! -d "${PROJDIR}/lib/AppImageUpdate-prebuilt" ]]; then
+if [ ! -d "${PROJDIR}/lib/AppImageUpdate-prebuilt" ]; then
     mkdir "${PROJDIR}/lib/AppImageUpdate-prebuilt"
     cd "${PROJDIR}/lib/AppImageUpdate-prebuilt"
     cmake "${PROJDIR}/lib/AppImageUpdate" -DBUILD_QT_UI=OFF -DCMAKE_BUILD_TYPE=RelWithDebInfo