Update doc/install/installation.md

**Line 295: sudo /etc/init.d/gitlab restart**
Results in: "Error, unicorn not running!"
This is because unicorn is not yet running for first boot. I suggest changing this to 'start'.

**Line 305: sudo apt-get install nginx**
Change command to: sudo apt-get -y install nginx
Allowing automated install to simplify and follow pattern of earlier installs.