Due issue #27 (Tiny backpack due resizing screen)

As solution for issue https://github.com/ROBLOX/Core-Scripts/issues/27 opened by matthewdean.

As the GetScreenResolution() returns the real screen's resolution, and not just
the resolution of the roblox player, this will work to check if it's a phone.
(Unless someone uses a resolution on pc with a height of 320 or less, if that's possible)