examples: Update `winit` requirement to `0.30`

[fryeb]

Supersedes #914 (since 0.30 has breaking changes it requires some code changes).

[Ralith]

I'd merge this, but both it and master fail on my (NixOS) machine with:

thread 'main' panicked at /home/ralith/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/x11-dl-2.19.1/src/xlib.rs:25:1:
null pointer dereference occurred

so I'd better wait for someone else to test.