Feature: Move TS compiler target from ES6 to ES5

[ninjaPixel]

The typescript is transpilled to ES6 which means that older browsers throw an error when they try to load it.

Would you be open to a pull request to change the TypeScript compiler target from ES6 to ES5?

[quinnlangille]

Hey @ninjaPixel, this repo isn't currently maintained by anyone so sorry for the long wait. However, this seems like a small and pretty reasonable request, so if you're still up for making the PR be my guest. Otherwise, I'll take care of it when I get a second