fix(installer): backup linked files with rsync (#2081)

This allows backup to succeed for people who use symlinks for managing dotfiles.

Currently errors with the following:
```
rsync error: some files/attrs were not transferred (see previous errors) (code 23) \
at main.c(1350) [sender=3.2.3]
````

utils/installer/install.sh

@@ -288,7 +288,7 @@ function backup_old_config() {
     touch "$dir/ignore"
     msg "Backing up old $dir to $dir.bak"
     if command -v rsync &>/dev/null; then
-      rsync --archive -hh --stats --partial --cvs-exclude "$dir"/ "$dir.bak"
+      rsync --archive -hh --stats --partial --copy-links --cvs-exclude "$dir"/ "$dir.bak"
     else
       OS="$(uname -s)"
       case "$OS" in