Hi Vu Phang,
I manually executed the following command from the script:
git clone git://git.denx.de/u-boot.git uboot-imx
I was able to clone the repository successfully. I am also able to resolve the name domain name 'git.denx.de' to the IP address 85.214.87.163 using ping (although the server doesn't respond to ICMP echo requests). The server will also supply the a web-based listing of the projects if you use a Browser to load 'git.denx.de'. In the header, it also indicates it will accept 'http://' as well as 'git://' which I confirmed makes a connection but seemed to stall trying to pull the data. Based on a quick review of the script, it should work for you unless there is a firewall issue using git.
Are you able to bring up 'git.denx.de' in your Browser?