RCON writecfg changes are reverted on restart

## User Story

Since installing rustserver on LGSM, the RCON `server.writecfg` changes will always revert on restart. This has occurred for multiple fields.

## Basic info

* **Distro:** Ubuntu 20.04.1
* **Game:** Rust
* **Command:** server.writecfg and ./rustserver restart
* **LinuxGSM version:** v20.4.1

## Further Information

Bug: `server.writecfg` command's changes are reverted on server restart
How to resolve: Input the data manually into the config file
Listed in the documentation here: https://docs.linuxgsm.com/game-servers/rust#essential-rcon-commands

## To Reproduce

Steps to reproduce the behaviour:
1. Go to the facepunch rcon page
2. Update a config value using the console
3. Write to config using `server.writecfg`
4. Restart server