Fixes #67 - Crash on macOS. piston_window version bump

[cuyler]

This brings in the bug fix from piston_window #227.

[sunjay]

Thanks for taking the time to look at this! The build seems to be failing for some reason on MacOS. Could you look into it?

I am happy to accept this PR over #78 if we can figure this out. Let me know how I can help! 😄

[jdm]

     Running `target/debug/examples/runtest`
thread 'main' panicked at 'bug: could not build window: "Couldn\'t find any pixel format that matches the criterias."', libcore/result.rs:945:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[sunjay]

Hmm that's not good. If you run cargo run --example runtest on Mac, is it reproducible? If so, that means that the bug probably isn't fixed. I don't have a Mac to look into this further.

[sunjay]

Hi! Thanks for attempting to solve this through this PR! It turns out that the solution is not as trivial as just bumping the piston version. They appear to have updated some dependencies in between their releases and that has blocked our ability to update to those versions. I do not actually know what is required to update successfully and since I do not have a Mac, I can't really spend time on this at the moment.

Over the past couple of weeks, I have pretty much given up on piston for the time being. If you or anyone else is still willing to look into this and get Mac support back, I am happy to merge a fix.

Hopefully we will be able to add complete cross-platform support back soon!