[BUG] Misnamed Arma 3 command-line parameters

## Basic info

* **Distro:** [Ubuntu Server 20.04 LTS]
* **Game:** [Arma 3]
* **Command:** [Details/Start]
* **LinuxGSM version:** [v21.2.3]

## Further Information

When reading [documentation](https://community.bistudio.com/wiki/Arma_3:_Startup_Parameters#Modifications) from Bohemia, server owners are told to use **-mod** or **-serverMod** to load mods onto their servers. However, LGSM requires them to be delcared in `arma3server.cfg` as **-mods** and **-serverMods** instead.

I think it would be a great idea to fix the variable names so server owners do not get confused/frustrated trying to figure out why LGSM is not taking their arguments.

## Steps

1. Take any Arma 3 mod (@CBA_A3 was used) and copy it to the **serverfiles** directory
2. In arma3server.cfg add **mod="@cba_a3"** to a new line, save changes.
3. Run **./arma3server dt**
4. Under command-line parameters, despite declaring it the **-mod** argument remains empty.
5. Modify arma3server.cfg to have **mods="@cba_a3"**, save and exit.
6. Run **./arma3server dt** again
7. See that **cba_a3** is a command-line argument for **-mod**