added missing nc command

[egandro]

The netcat command is missing in wait-for-it.sh.

When using the official docker container start.sh script has a race condition:

scripts/wait-for-it.sh ${DATABASE_HOST} -- echo "database is up" is not blocking the execution of the start process - the migrate command fails.

I think it was not discovered during your regular development process, as the database is always created during build time RUN yarn db-deploy.

My patch hopefully fixes the root cause of the official docker images.