--check-config breaks boostrap dns

Using the Lastest Stable Release when **--check-config** is run for the first time on a fresh meaning "new" .yaml file bootstrap resolver that are listed in

```
- 8.8.8.8
- 9.9.9.9
```

format gets changed to

```-'[8.8.8.8 9.9.9.9]'```

which the webui reports as an incorrect format.

Here is the output

```
2022/01/03 01:39:20.322742 [info] AdGuard Home, version v0.107.2
2022/01/03 01:39:20.442423 [info] home.upgradeSchema0to1(): called
2022/01/03 01:39:20.442484 [info] deleting /tmp/mnt/My_Part/entware/etc/AdGuardHome/dnsfilter.txt as we don't need it anymore
2022/01/03 01:39:20.442568 [info] home.upgradeSchema1to2(): called
2022/01/03 01:39:20.442586 [info] deleting /tmp/mnt/My_Part/entware/etc/AdGuardHome/Corefile as we don't need it anymore
2022/01/03 01:39:20.442624 [info] home.upgradeSchema2to3(): called
2022/01/03 01:39:20.442679 [info] home.upgradeSchema3to4(): called
2022/01/03 01:39:20.442705 [info] home.upgradeSchema4to5(): called
2022/01/03 01:39:20.442729 [info] home.upgradeSchema5to6(): called
2022/01/03 01:39:20.442744 [info] Upgrade yaml: 6 to 7
2022/01/03 01:39:20.442758 [info] Upgrade yaml: 7 to 8
2022/01/03 01:39:20.442777 [info] Upgrade yaml: 8 to 9
2022/01/03 01:39:20.442792 [info] Upgrade yaml: 9 to 10
2022/01/03 01:39:20.442820 [info] Upgrade yaml: 10 to 11
2022/01/03 01:39:20.442838 [info] Upgrade yaml: 11 to 12
2022/01/03 01:39:20.449652 [info] configuration file is ok
```

In side the .yaml file, the bootstrap resolvers have been changed from

```
- 8.8.8.8
- 9.9.9.9
```

to

```
-'[8.8.8.8 9.9.9.9]'
```