[BUG] Valheim backups fail on first use, lgsm docs provide inconsistent information.

## User Story

As a server owner, I want backup the gameserver & world without needing to problem solve and refer to incorrect documents so that backups are completed without issue.

## Basic info

* **Distro:** [Ubuntu 20.04]
* **Game:** [Valheim]
* **Command:** [Backup]
* **LinuxGSM version:** [v21.1.3]

## Further Information

I tried to backup the valheim server and was presented with:
```
[ OK ] Backing up vhserver: Backup starting
[ INFO ] Backing up vhserver: There are no previous backups
[ FAIL ] Backing up vhserver: Problem identifying the previous backup directory for exclusion.
```

I read lgsm doc's which states:
```
├── home
├── csgoserver
├── ** backups **
├── lgsm
├── log
├── serverfiles
```

and when comparing this to my installation, I saw no such directory. Given this, and the error, I decided to create it, and ran the backup again:

`[ INFO ] Backing up vhserver: Lock file found: Backup is currently running`

Deleted the lock file inside of `~/lgsm/locks/` and ran the backup again:

```
[ OK ] Backing up vhserver: Backup starting
[ INFO ] Backing up vhserver: There are no previous backups
[ ERROR ] Backing up vhserver: Backup directory is being migrated
[ OK ] Backing up vhserver: Completed: vhserver-2021-02-15-063904.tar.gz, total size 772M
```

Then, when looking for my backup, I discovered the `~/backups` directory was empty, and when asking on the discord, I was directed inside of `~/lgsm/backups` which is inconsistent with the lgsm docs.

## To Reproduce

Steps to reproduce the behaviour:
Install valheim server, using the documented setup.
Configure server with server name and password via vhserver.cfg
start the server
stop the server
backup the server -> see above issue

## Expected behaviour
Install valheim server, using the documented setup.
Configure server with server name and password via vhserver.cfg
start the server
stop the server
backup the server completes successfully.