The glutin/winit update in #700 changed set_cursor_grab from a bool to
an enum, but always used CursorGrabMode::Locked, which is only available
on macOS. Conditionally compile to use CursorGrabMode::Confined otherwise.
Fixes#714 and fixes#713
* set_cursor_grab failed with NotSupported(NotSupportedError) on Linux
Patch from https://github.com/iceiix/stevenarella/issues/714
* cargo fmt
Co-authored-by: inferno <inferrna@gmail.com>