Currently the environment-setup.sh developer script will fail if it is run in a network environment that only provides internet access via an HTTP(S) proxy service(in my case is the usage of TetherFi but it may also occur in company networks that are heavily monitored).
I’ve already made a patch that enables me to run the script without issues, if no one has any problems with it I’ll file a pull request to get it (hopefully) merged to the project.