After performing git push -u origin master, I got:
git push -u origin master
fatal: unable to access \'https://github.com/xxxx/xxxx.git
It seems that git tries to use a local proxy.
Please check your global network-settings and those of git.
Use git config http.proxy and git config --global http.proxy to get the proxy-settings of git.
git config http.proxy
git config --global http.proxy