support trying out SB with a single command

[msukkari]

• pulls in new zoekt version that supports pulling in public github repos when no token is provided

one-command working using:

 docker build -t sourcebot .
 docker run -p 3000:3000 --rm --name sourcebot -v ./sample-config.json:/app/sample-config.json -e CONFIG_PATH=sample-config.json sourcebot