Fix #217 - Change systemd-service type to forking

Besides user-feedback I've found many resources showing that it is one common way to use forking here.
I've also found the option "--nofork" for i3lock-color but I'm unsure of the side-effects.

https://gist.github.com/victorhaggqvist/603125bbc0f61a787d89
https://www.jvt.me/posts/2019/12/03/lock-before-suspend-systemd/
https://michaelabrahamsen.com/posts/systemd-suspend-i3lock/

system/betterlockscreen@.service

@@ -5,7 +5,7 @@ Before=suspend.target
 
 [Service]
 User=%I
-Type=simple
+Type=forking
 Environment=DISPLAY=:0
 ExecStart=/usr/local/bin/betterlockscreen --lock
 TimeoutSec=infinity