Update and simplify snake_game.js game engine (2 liner)

[nickolasnikolic]

Hi there!

I noted that the snake died a little early in some longer games, so I reworked the game engine to allow for longer snakes. It's now simplified to an additional array that is run through to see if the snake head has already been there. Thank you for your work!

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.