Quick fix on the installation script

[ShironCat]

I just installed winetricks on my machine and, in doing so, I've faced a small problem with the script. The systemd service created gives an error 203.

After searching a bit, I figured the problem is in this line:

ExecStart=/usr/bin/update_winetricks

According to this post on StackOverflow, this line should be ExecStart=/bin/bash /usr/bin/update_winetricks instead.

I am aware that a rewrite of the README install section is being discussed on #1192, but since this problem has such an easy solution, I'll submit a PR to fix this while that is done.

[austin987]

Fixed.