Update motd path in startup.lua

Removes situations where shell resolution caused arbitrary program called `motd` at root get executed instead of expected /rom one.

projects/core/src/main/resources/data/computercraft/lua/rom/startup.lua

@@ -191,7 +191,7 @@ end
 
 -- Show MOTD
 if settings.get("motd.enable") then
-    shell.run("motd")
+    shell.run("/rom/programs/motd")
 end
 
 -- Run the user created startup, either from disk drives or the root