Cannot Change Docker Size on Ubuntu 16.04
The only log message there is "Start request repeated too quickly." so we're missing the beginning of the error. You can run as root systemctl reset-failed and then systemctl start docker followed by journalctl -u docker --no-pager -n 50 to show the last 50 lines of logs.

Most likely, your problem is that your storage driver is not device mapper, and this option only applies to device mapper. On an 18.03 install, ubuntu will be overlay2 with a recent enough kernel, or possibly aufs on older kernels. Without using the device mapper storage driver, you should not be setting that option.