joyent repo is hardcoded in a few places

[nfitch]

Makes it harder for people to clone the repo and check that changes work before submitting pull requests.

nate@nateee:~/projects/minecrab$ find . -type f | xargs grep joyent/minecrab
./scripts/bootstrap.sh:/opt/local/bin/git clone https://github.com/joyent/minecrab.git
./scripts/map.sh:  init_script="https://raw.github.com/joyent/minecrab/master/scripts/prepare_render.sh"
./bin/minecrab-map:#INIT_SCRIPT="https://raw.github.com/joyent/minecrab/master/scripts/prepare_render.sh"
./bin/minecrab-launch:server_execute "cd /opt && git clone https://github.com/joyent/minecrab.git"
./README.md:   git clone https://github.com/joyent/minecrab.git