Update nginx-boot.sh to change root to nginx user

[MarkErik]

Run the nginx process, and file ownership as nginx rather than root.

[MarkErik]

From what I understand, if possible it is best to run as few things as possible with the root user.

However, from what I read, nginx gets started by root, and then spawns a second process that has less privileges - and so this PR may be a moot point. But it seems like it can't hurt to have nginx running from the start as the nginx user.

*Original
PID USER TIME COMMAND
1 root 0:00 nginx: master process nginx -c /etc/nginx/mushed.conf
11 root 0:00 nginx: worker process
12 root 0:00 bash
18 root 0:00 ps

*Proposed change
1 root 0:00 nginx: master process nginx -c /etc/nginx/mushed.conf
11 nginx 0:00 nginx: worker process
12 root 0:00 bash
18 root 0:00 ps

[MarkErik]

@cusspvz I was wondering if you'd be willing to accept this PR into the project. I've been using it for a while and it works fine.