fix(mac_shortcut.sh): fix shellcheck error

```bash
In postgres/templates/mac_shortcut.sh line 3:
shortcutName='${1}'
             ^----^ SC2016: Expressions don't expand in single quotes, use double quotes for that.
```

postgres/templates/mac_shortcut.sh

@@ -1,8 +1,7 @@
 #!/usr/bin/env bash
 
-shortcutName='${1}'
+shortcutName="${1}"
 app="postgres.app"
 Source="/Applications/$app"
 Destination="{{ homes }}/{{ user }}/Desktop/${shortcutName}"
 /usr/bin/osascript -e "tell application \"Finder\" to make alias file to POSIX file \"$Source\" at POSIX file \"$Destination\""
-