Fix open path in qubes-open-file-manager.desktop

Looks like desktop entries doesn`t allow environment variables in Exec string.
qubes.StartApp+qubes-open-file-manager-dom0[1782]: gio: file:///home/user/$HOME: Error when getting information for file “/home/user/$HOME”: No such file or directory

switching to '.' resolve it.

app-menu/qubes-open-file-manager.desktop

@@ -1,5 +1,5 @@
 [Desktop Entry]
 Name=Run Terminal
-Exec=xdg-open $HOME
+Exec=xdg-open .
 Icon=system-file-manager
 Type=Application