git clone --mirror git@bitbucket.org:username/deploy.git
cd deploy.git
GIT_WORK_TREE=/var/www/deploy.example.com git checkout -f master

sudo chown -R username:www-data /var/www
sudo chown -R username:www-data deploy.git

cd ~/deploy.git
git fetch
GIT_WORK_TREE=/var/www/deploy.example.com git checkout -f