Asking user if we should upgrade on arch install.

pacman -Sy can cause dependency problems and conflicts, as noted in #944 

So, this replaces pacman -Sy with -Syu (system upgrade), but prompts the user as to whether they want to upgrade and warns that if they haven't updated their package list recently, downloads/installing may fail. 
this is actually better like this

```bash
if [[ $updateVar =~ ^([yY][eE][sS]|[yY])$ ]]; then
```

and that way we keep it consistent to the way we ask for 'y,Y,yes,YES,Yes...'