Revert yarnpkg#1553 and instead just use Bash explicitly (yarnpkg#1580)

Author: Daniel15

scripts/install-latest.sh

@@ -1,11 +1,11 @@
-#!/bin/sh
+#!/bin/bash
 set -e
 
-reset=`tput sgr0`
-red=`tput setaf 1`
-green=`tput setaf 2`
-cyan=`tput setaf 6`
-white=`tput setaf 7`
+reset="\e[0m"
+red="\e[0;31m"
+green="\e[0;32m"
+cyan="\e[0;36m"
+white="\e[0;37m"
 
 yarn_get_tarball() {
   printf "$cyan> Downloading tarball...$reset\n"