Fix entrypoint.sh to run app with main PID

Using exec to call `node main` ensures that SIGTERM and SIGINT are
propagated to the app when the container is requested to shut down.

docker/entrypoint.sh

@@ -9,4 +9,4 @@ echo "Seeding the database"
 npx prisma db seed
 
 echo "Starting the server"
-node main
+exec node main